* [PATCH] PcAtChipsetPkg AcpiTimerLib: Wait 363 ACPI timer counts to get TSC Freq
@ 2016-08-17 2:26 Star Zeng
2016-08-17 10:31 ` Paolo Bonzini
2016-08-17 15:49 ` Kinney, Michael D
0 siblings, 2 replies; 4+ messages in thread
From: Star Zeng @ 2016-08-17 2:26 UTC (permalink / raw)
To: edk2-devel
Cc: Star Zeng, Michael D Kinney, Liming Gao, Paolo Bonzini,
Paul A Lohr
Compute the number of ticks to wait to measure TSC frequency.
Instead of (ACPI_TIMER_FREQUENCY / 10000) = 357 and 357 * 10000 = 3570000,
use 363 * 9861 = 3579543 Hz which is within 2 Hz of ACPI_TIMER_FREQUENCY.
363 counts is a calibration time of 101.4 uS.
The idea comes from Michael and Paolo.
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Paul A Lohr <paul.a.lohr@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
---
PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c | 32 +++++++++++++---------
.../Library/AcpiTimerLib/BaseAcpiTimerLib.c | 14 +++++-----
.../Library/AcpiTimerLib/DxeAcpiTimerLib.c | 14 +++++-----
3 files changed, 33 insertions(+), 27 deletions(-)
diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c b/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
index e6fea231123d..020031e3f4a5 100644
--- a/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
+++ b/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
@@ -340,13 +340,13 @@ GetTimeInNanoSecond (
Calculate TSC frequency.
The TSC counting frequency is determined by comparing how far it counts
- during a 100us period as determined by the ACPI timer. The ACPI timer is
- used because it counts at a known frequency.
- The TSC is sampled, followed by waiting for ACPI_TIMER_FREQUENCY / 10000
- clocks of the ACPI timer, or 100us. The TSC is then sampled again. The
- difference multiplied by 10000 is the TSC frequency. There will be a small
- error because of the overhead of reading the ACPI timer. An attempt is
- made to determine and compensate for this error.
+ during a 101.4 us period as determined by the ACPI timer.
+ The ACPI timer is used because it counts at a known frequency.
+ The TSC is sampled, followed by waiting 363 counts of the ACPI timer,
+ or 101.4 us. The TSC is then sampled again. The difference multiplied by
+ 9861 is the TSC frequency. There will be a small error because of the
+ overhead of reading the ACPI timer. An attempt is made to determine and
+ compensate for this error.
@return The number of TSC counts per second.
@@ -366,22 +366,28 @@ InternalCalculateTscFrequency (
InterruptState = SaveAndDisableInterrupts ();
TimerAddr = InternalAcpiGetAcpiTimerIoPort ();
- Ticks = IoRead32 (TimerAddr) + (ACPI_TIMER_FREQUENCY / 10000); // Set Ticks to 100us in the future
+ //
+ // Compute the number of ticks to wait to measure TSC frequency.
+ // Use 363 * 9861 = 3579543 Hz which is within 2 Hz of ACPI_TIMER_FREQUENCY.
+ // 363 counts is a calibration time of 101.4 uS.
+ //
+ Ticks = IoRead32 (TimerAddr) + 363;
StartTSC = AsmReadTsc (); // Get base value for the TSC
//
- // Wait until the ACPI timer has counted 100us.
+ // Wait until the ACPI timer has counted 101.4 us.
// Timer wrap-arounds are handled correctly by this function.
- // When the current ACPI timer value is greater than 'Ticks', the while loop will exit.
+ // When the current ACPI timer value is greater than 'Ticks',
+ // the while loop will exit.
//
while (((Ticks - IoRead32 (TimerAddr)) & BIT23) == 0) {
CpuPause();
}
- EndTSC = AsmReadTsc (); // TSC value 100us later
+ EndTSC = AsmReadTsc (); // TSC value 101.4 us later
TscFrequency = MultU64x32 (
- (EndTSC - StartTSC), // Number of TSC counts in 100us
- 10000 // Number of 100us in a second
+ (EndTSC - StartTSC), // Number of TSC counts in 101.4 us
+ 9861 // Number of 101.4 us in a second
);
SetInterruptState (InterruptState);
diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c b/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
index 8819ebcfccef..29521f8b220b 100644
--- a/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
+++ b/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
@@ -20,13 +20,13 @@
Calculate TSC frequency.
The TSC counting frequency is determined by comparing how far it counts
- during a 100us period as determined by the ACPI timer. The ACPI timer is
- used because it counts at a known frequency.
- The TSC is sampled, followed by waiting for ACPI_TIMER_FREQUENCY / 10000
- clocks of the ACPI timer, or 100us. The TSC is then sampled again. The
- difference multiplied by 10000 is the TSC frequency. There will be a small
- error because of the overhead of reading the ACPI timer. An attempt is
- made to determine and compensate for this error.
+ during a 101.4 us period as determined by the ACPI timer.
+ The ACPI timer is used because it counts at a known frequency.
+ The TSC is sampled, followed by waiting 363 counts of the ACPI timer,
+ or 101.4 us. The TSC is then sampled again. The difference multiplied by
+ 9861 is the TSC frequency. There will be a small error because of the
+ overhead of reading the ACPI timer. An attempt is made to determine and
+ compensate for this error.
@return The number of TSC counts per second.
diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c b/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c
index 7f7b0f8f6294..b141c680fb82 100644
--- a/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c
+++ b/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c
@@ -20,13 +20,13 @@
Calculate TSC frequency.
The TSC counting frequency is determined by comparing how far it counts
- during a 100us period as determined by the ACPI timer. The ACPI timer is
- used because it counts at a known frequency.
- The TSC is sampled, followed by waiting for ACPI_TIMER_FREQUENCY / 10000
- clocks of the ACPI timer, or 100us. The TSC is then sampled again. The
- difference multiplied by 10000 is the TSC frequency. There will be a small
- error because of the overhead of reading the ACPI timer. An attempt is
- made to determine and compensate for this error.
+ during a 101.4 us period as determined by the ACPI timer.
+ The ACPI timer is used because it counts at a known frequency.
+ The TSC is sampled, followed by waiting 363 counts of the ACPI timer,
+ or 101.4 us. The TSC is then sampled again. The difference multiplied by
+ 9861 is the TSC frequency. There will be a small error because of the
+ overhead of reading the ACPI timer. An attempt is made to determine and
+ compensate for this error.
@return The number of TSC counts per second.
--
2.7.0.windows.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] PcAtChipsetPkg AcpiTimerLib: Wait 363 ACPI timer counts to get TSC Freq
2016-08-17 2:26 [PATCH] PcAtChipsetPkg AcpiTimerLib: Wait 363 ACPI timer counts to get TSC Freq Star Zeng
@ 2016-08-17 10:31 ` Paolo Bonzini
2016-08-17 15:47 ` Kinney, Michael D
2016-08-17 15:49 ` Kinney, Michael D
1 sibling, 1 reply; 4+ messages in thread
From: Paolo Bonzini @ 2016-08-17 10:31 UTC (permalink / raw)
To: Star Zeng, edk2-devel; +Cc: Michael D Kinney, Liming Gao
On 17/08/2016 04:26, Star Zeng wrote:
> Compute the number of ticks to wait to measure TSC frequency.
> Instead of (ACPI_TIMER_FREQUENCY / 10000) = 357 and 357 * 10000 = 3570000,
> use 363 * 9861 = 3579543 Hz which is within 2 Hz of ACPI_TIMER_FREQUENCY.
> 363 counts is a calibration time of 101.4 uS.
>
> The idea comes from Michael and Paolo.
>
> Cc: Michael D Kinney <michael.d.kinney@intel.com>
> Cc: Liming Gao <liming.gao@intel.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Paul A Lohr <paul.a.lohr@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Star Zeng <star.zeng@intel.com>
> ---
> PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c | 32 +++++++++++++---------
> .../Library/AcpiTimerLib/BaseAcpiTimerLib.c | 14 +++++-----
> .../Library/AcpiTimerLib/DxeAcpiTimerLib.c | 14 +++++-----
> 3 files changed, 33 insertions(+), 27 deletions(-)
>
> diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c b/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
> index e6fea231123d..020031e3f4a5 100644
> --- a/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
> +++ b/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
> @@ -340,13 +340,13 @@ GetTimeInNanoSecond (
> Calculate TSC frequency.
>
> The TSC counting frequency is determined by comparing how far it counts
> - during a 100us period as determined by the ACPI timer. The ACPI timer is
> - used because it counts at a known frequency.
> - The TSC is sampled, followed by waiting for ACPI_TIMER_FREQUENCY / 10000
> - clocks of the ACPI timer, or 100us. The TSC is then sampled again. The
> - difference multiplied by 10000 is the TSC frequency. There will be a small
> - error because of the overhead of reading the ACPI timer. An attempt is
> - made to determine and compensate for this error.
> + during a 101.4 us period as determined by the ACPI timer.
> + The ACPI timer is used because it counts at a known frequency.
> + The TSC is sampled, followed by waiting 363 counts of the ACPI timer,
> + or 101.4 us. The TSC is then sampled again. The difference multiplied by
> + 9861 is the TSC frequency. There will be a small error because of the
> + overhead of reading the ACPI timer. An attempt is made to determine and
> + compensate for this error.
>
> @return The number of TSC counts per second.
>
> @@ -366,22 +366,28 @@ InternalCalculateTscFrequency (
> InterruptState = SaveAndDisableInterrupts ();
>
> TimerAddr = InternalAcpiGetAcpiTimerIoPort ();
> - Ticks = IoRead32 (TimerAddr) + (ACPI_TIMER_FREQUENCY / 10000); // Set Ticks to 100us in the future
> + //
> + // Compute the number of ticks to wait to measure TSC frequency.
> + // Use 363 * 9861 = 3579543 Hz which is within 2 Hz of ACPI_TIMER_FREQUENCY.
> + // 363 counts is a calibration time of 101.4 uS.
> + //
> + Ticks = IoRead32 (TimerAddr) + 363;
>
> StartTSC = AsmReadTsc (); // Get base value for the TSC
> //
> - // Wait until the ACPI timer has counted 100us.
> + // Wait until the ACPI timer has counted 101.4 us.
> // Timer wrap-arounds are handled correctly by this function.
> - // When the current ACPI timer value is greater than 'Ticks', the while loop will exit.
> + // When the current ACPI timer value is greater than 'Ticks',
> + // the while loop will exit.
> //
> while (((Ticks - IoRead32 (TimerAddr)) & BIT23) == 0) {
> CpuPause();
> }
> - EndTSC = AsmReadTsc (); // TSC value 100us later
> + EndTSC = AsmReadTsc (); // TSC value 101.4 us later
>
> TscFrequency = MultU64x32 (
> - (EndTSC - StartTSC), // Number of TSC counts in 100us
> - 10000 // Number of 100us in a second
> + (EndTSC - StartTSC), // Number of TSC counts in 101.4 us
> + 9861 // Number of 101.4 us in a second
> );
>
> SetInterruptState (InterruptState);
> diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c b/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
> index 8819ebcfccef..29521f8b220b 100644
> --- a/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
> +++ b/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
> @@ -20,13 +20,13 @@
> Calculate TSC frequency.
>
> The TSC counting frequency is determined by comparing how far it counts
> - during a 100us period as determined by the ACPI timer. The ACPI timer is
> - used because it counts at a known frequency.
> - The TSC is sampled, followed by waiting for ACPI_TIMER_FREQUENCY / 10000
> - clocks of the ACPI timer, or 100us. The TSC is then sampled again. The
> - difference multiplied by 10000 is the TSC frequency. There will be a small
> - error because of the overhead of reading the ACPI timer. An attempt is
> - made to determine and compensate for this error.
> + during a 101.4 us period as determined by the ACPI timer.
> + The ACPI timer is used because it counts at a known frequency.
> + The TSC is sampled, followed by waiting 363 counts of the ACPI timer,
> + or 101.4 us. The TSC is then sampled again. The difference multiplied by
> + 9861 is the TSC frequency. There will be a small error because of the
> + overhead of reading the ACPI timer. An attempt is made to determine and
> + compensate for this error.
>
> @return The number of TSC counts per second.
>
> diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c b/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c
> index 7f7b0f8f6294..b141c680fb82 100644
> --- a/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c
> +++ b/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c
> @@ -20,13 +20,13 @@
> Calculate TSC frequency.
>
> The TSC counting frequency is determined by comparing how far it counts
> - during a 100us period as determined by the ACPI timer. The ACPI timer is
> - used because it counts at a known frequency.
> - The TSC is sampled, followed by waiting for ACPI_TIMER_FREQUENCY / 10000
> - clocks of the ACPI timer, or 100us. The TSC is then sampled again. The
> - difference multiplied by 10000 is the TSC frequency. There will be a small
> - error because of the overhead of reading the ACPI timer. An attempt is
> - made to determine and compensate for this error.
> + during a 101.4 us period as determined by the ACPI timer.
> + The ACPI timer is used because it counts at a known frequency.
> + The TSC is sampled, followed by waiting 363 counts of the ACPI timer,
> + or 101.4 us. The TSC is then sampled again. The difference multiplied by
> + 9861 is the TSC frequency. There will be a small error because of the
> + overhead of reading the ACPI timer. An attempt is made to determine and
> + compensate for this error.
>
> @return The number of TSC counts per second.
>
>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
On top of this you can add the logic to wait for the beginning of a tick
before calling rdtsc.
Paolo
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] PcAtChipsetPkg AcpiTimerLib: Wait 363 ACPI timer counts to get TSC Freq
2016-08-17 10:31 ` Paolo Bonzini
@ 2016-08-17 15:47 ` Kinney, Michael D
0 siblings, 0 replies; 4+ messages in thread
From: Kinney, Michael D @ 2016-08-17 15:47 UTC (permalink / raw)
To: Paolo Bonzini, Zeng, Star, edk2-devel@lists.01.org,
Kinney, Michael D
Cc: Gao, Liming
Hi Paolo,
We did some experiments to wait for the next ACPI Timer tick, and they did
not improve the results.
On real HW, the I/O Port read of the ACPI Timer takes ~1 uS, and an ACPI Timer
tick is about 0.25 uS, so the action to read the counter takes 4 times longer
than a single count.
If the I/O port read was much faster than the tick period, then adding the loop
would make sense.
Mike
> -----Original Message-----
> From: Paolo Bonzini [mailto:paolo.bonzini@gmail.com] On Behalf Of Paolo Bonzini
> Sent: Wednesday, August 17, 2016 3:31 AM
> To: Zeng, Star <star.zeng@intel.com>; edk2-devel@lists.01.org
> Cc: Kinney, Michael D <michael.d.kinney@intel.com>; Gao, Liming
> <liming.gao@intel.com>
> Subject: Re: [edk2] [PATCH] PcAtChipsetPkg AcpiTimerLib: Wait 363 ACPI timer counts
> to get TSC Freq
>
>
>
> On 17/08/2016 04:26, Star Zeng wrote:
> > Compute the number of ticks to wait to measure TSC frequency.
> > Instead of (ACPI_TIMER_FREQUENCY / 10000) = 357 and 357 * 10000 = 3570000,
> > use 363 * 9861 = 3579543 Hz which is within 2 Hz of ACPI_TIMER_FREQUENCY.
> > 363 counts is a calibration time of 101.4 uS.
> >
> > The idea comes from Michael and Paolo.
> >
> > Cc: Michael D Kinney <michael.d.kinney@intel.com>
> > Cc: Liming Gao <liming.gao@intel.com>
> > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > Cc: Paul A Lohr <paul.a.lohr@intel.com>
> > Contributed-under: TianoCore Contribution Agreement 1.0
> > Signed-off-by: Star Zeng <star.zeng@intel.com>
> > ---
> > PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c | 32 +++++++++++++---------
> > .../Library/AcpiTimerLib/BaseAcpiTimerLib.c | 14 +++++-----
> > .../Library/AcpiTimerLib/DxeAcpiTimerLib.c | 14 +++++-----
> > 3 files changed, 33 insertions(+), 27 deletions(-)
> >
> > diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
> b/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
> > index e6fea231123d..020031e3f4a5 100644
> > --- a/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
> > +++ b/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
> > @@ -340,13 +340,13 @@ GetTimeInNanoSecond (
> > Calculate TSC frequency.
> >
> > The TSC counting frequency is determined by comparing how far it counts
> > - during a 100us period as determined by the ACPI timer. The ACPI timer is
> > - used because it counts at a known frequency.
> > - The TSC is sampled, followed by waiting for ACPI_TIMER_FREQUENCY / 10000
> > - clocks of the ACPI timer, or 100us. The TSC is then sampled again. The
> > - difference multiplied by 10000 is the TSC frequency. There will be a small
> > - error because of the overhead of reading the ACPI timer. An attempt is
> > - made to determine and compensate for this error.
> > + during a 101.4 us period as determined by the ACPI timer.
> > + The ACPI timer is used because it counts at a known frequency.
> > + The TSC is sampled, followed by waiting 363 counts of the ACPI timer,
> > + or 101.4 us. The TSC is then sampled again. The difference multiplied by
> > + 9861 is the TSC frequency. There will be a small error because of the
> > + overhead of reading the ACPI timer. An attempt is made to determine and
> > + compensate for this error.
> >
> > @return The number of TSC counts per second.
> >
> > @@ -366,22 +366,28 @@ InternalCalculateTscFrequency (
> > InterruptState = SaveAndDisableInterrupts ();
> >
> > TimerAddr = InternalAcpiGetAcpiTimerIoPort ();
> > - Ticks = IoRead32 (TimerAddr) + (ACPI_TIMER_FREQUENCY / 10000); // Set Ticks
> to 100us in the future
> > + //
> > + // Compute the number of ticks to wait to measure TSC frequency.
> > + // Use 363 * 9861 = 3579543 Hz which is within 2 Hz of ACPI_TIMER_FREQUENCY.
> > + // 363 counts is a calibration time of 101.4 uS.
> > + //
> > + Ticks = IoRead32 (TimerAddr) + 363;
> >
> > StartTSC = AsmReadTsc (); // Get base
> value for the TSC
> > //
> > - // Wait until the ACPI timer has counted 100us.
> > + // Wait until the ACPI timer has counted 101.4 us.
> > // Timer wrap-arounds are handled correctly by this function.
> > - // When the current ACPI timer value is greater than 'Ticks', the while loop
> will exit.
> > + // When the current ACPI timer value is greater than 'Ticks',
> > + // the while loop will exit.
> > //
> > while (((Ticks - IoRead32 (TimerAddr)) & BIT23) == 0) {
> > CpuPause();
> > }
> > - EndTSC = AsmReadTsc (); // TSC value
> 100us later
> > + EndTSC = AsmReadTsc (); // TSC value
> 101.4 us later
> >
> > TscFrequency = MultU64x32 (
> > - (EndTSC - StartTSC), // Number of
> TSC counts in 100us
> > - 10000 // Number of
> 100us in a second
> > + (EndTSC - StartTSC), // Number of
> TSC counts in 101.4 us
> > + 9861 // Number of
> 101.4 us in a second
> > );
> >
> > SetInterruptState (InterruptState);
> > diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
> b/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
> > index 8819ebcfccef..29521f8b220b 100644
> > --- a/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
> > +++ b/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
> > @@ -20,13 +20,13 @@
> > Calculate TSC frequency.
> >
> > The TSC counting frequency is determined by comparing how far it counts
> > - during a 100us period as determined by the ACPI timer. The ACPI timer is
> > - used because it counts at a known frequency.
> > - The TSC is sampled, followed by waiting for ACPI_TIMER_FREQUENCY / 10000
> > - clocks of the ACPI timer, or 100us. The TSC is then sampled again. The
> > - difference multiplied by 10000 is the TSC frequency. There will be a small
> > - error because of the overhead of reading the ACPI timer. An attempt is
> > - made to determine and compensate for this error.
> > + during a 101.4 us period as determined by the ACPI timer.
> > + The ACPI timer is used because it counts at a known frequency.
> > + The TSC is sampled, followed by waiting 363 counts of the ACPI timer,
> > + or 101.4 us. The TSC is then sampled again. The difference multiplied by
> > + 9861 is the TSC frequency. There will be a small error because of the
> > + overhead of reading the ACPI timer. An attempt is made to determine and
> > + compensate for this error.
> >
> > @return The number of TSC counts per second.
> >
> > diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c
> b/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c
> > index 7f7b0f8f6294..b141c680fb82 100644
> > --- a/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c
> > +++ b/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c
> > @@ -20,13 +20,13 @@
> > Calculate TSC frequency.
> >
> > The TSC counting frequency is determined by comparing how far it counts
> > - during a 100us period as determined by the ACPI timer. The ACPI timer is
> > - used because it counts at a known frequency.
> > - The TSC is sampled, followed by waiting for ACPI_TIMER_FREQUENCY / 10000
> > - clocks of the ACPI timer, or 100us. The TSC is then sampled again. The
> > - difference multiplied by 10000 is the TSC frequency. There will be a small
> > - error because of the overhead of reading the ACPI timer. An attempt is
> > - made to determine and compensate for this error.
> > + during a 101.4 us period as determined by the ACPI timer.
> > + The ACPI timer is used because it counts at a known frequency.
> > + The TSC is sampled, followed by waiting 363 counts of the ACPI timer,
> > + or 101.4 us. The TSC is then sampled again. The difference multiplied by
> > + 9861 is the TSC frequency. There will be a small error because of the
> > + overhead of reading the ACPI timer. An attempt is made to determine and
> > + compensate for this error.
> >
> > @return The number of TSC counts per second.
> >
> >
>
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
>
> On top of this you can add the logic to wait for the beginning of a tick
> before calling rdtsc.
>
> Paolo
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] PcAtChipsetPkg AcpiTimerLib: Wait 363 ACPI timer counts to get TSC Freq
2016-08-17 2:26 [PATCH] PcAtChipsetPkg AcpiTimerLib: Wait 363 ACPI timer counts to get TSC Freq Star Zeng
2016-08-17 10:31 ` Paolo Bonzini
@ 2016-08-17 15:49 ` Kinney, Michael D
1 sibling, 0 replies; 4+ messages in thread
From: Kinney, Michael D @ 2016-08-17 15:49 UTC (permalink / raw)
To: Zeng, Star, edk2-devel@lists.01.org, Kinney, Michael D
Cc: Gao, Liming, Paolo Bonzini, Lohr, Paul A
Reviewed-by: Michael Kinney <michael.d.kinney@intel.com>
> -----Original Message-----
> From: Zeng, Star
> Sent: Tuesday, August 16, 2016 7:27 PM
> To: edk2-devel@lists.01.org
> Cc: Zeng, Star <star.zeng@intel.com>; Kinney, Michael D <michael.d.kinney@intel.com>;
> Gao, Liming <liming.gao@intel.com>; Paolo Bonzini <pbonzini@redhat.com>; Lohr, Paul A
> <paul.a.lohr@intel.com>
> Subject: [PATCH] PcAtChipsetPkg AcpiTimerLib: Wait 363 ACPI timer counts to get TSC
> Freq
>
> Compute the number of ticks to wait to measure TSC frequency.
> Instead of (ACPI_TIMER_FREQUENCY / 10000) = 357 and 357 * 10000 = 3570000,
> use 363 * 9861 = 3579543 Hz which is within 2 Hz of ACPI_TIMER_FREQUENCY.
> 363 counts is a calibration time of 101.4 uS.
>
> The idea comes from Michael and Paolo.
>
> Cc: Michael D Kinney <michael.d.kinney@intel.com>
> Cc: Liming Gao <liming.gao@intel.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Paul A Lohr <paul.a.lohr@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Star Zeng <star.zeng@intel.com>
> ---
> PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c | 32 +++++++++++++---------
> .../Library/AcpiTimerLib/BaseAcpiTimerLib.c | 14 +++++-----
> .../Library/AcpiTimerLib/DxeAcpiTimerLib.c | 14 +++++-----
> 3 files changed, 33 insertions(+), 27 deletions(-)
>
> diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
> b/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
> index e6fea231123d..020031e3f4a5 100644
> --- a/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
> +++ b/PcAtChipsetPkg/Library/AcpiTimerLib/AcpiTimerLib.c
> @@ -340,13 +340,13 @@ GetTimeInNanoSecond (
> Calculate TSC frequency.
>
> The TSC counting frequency is determined by comparing how far it counts
> - during a 100us period as determined by the ACPI timer. The ACPI timer is
> - used because it counts at a known frequency.
> - The TSC is sampled, followed by waiting for ACPI_TIMER_FREQUENCY / 10000
> - clocks of the ACPI timer, or 100us. The TSC is then sampled again. The
> - difference multiplied by 10000 is the TSC frequency. There will be a small
> - error because of the overhead of reading the ACPI timer. An attempt is
> - made to determine and compensate for this error.
> + during a 101.4 us period as determined by the ACPI timer.
> + The ACPI timer is used because it counts at a known frequency.
> + The TSC is sampled, followed by waiting 363 counts of the ACPI timer,
> + or 101.4 us. The TSC is then sampled again. The difference multiplied by
> + 9861 is the TSC frequency. There will be a small error because of the
> + overhead of reading the ACPI timer. An attempt is made to determine and
> + compensate for this error.
>
> @return The number of TSC counts per second.
>
> @@ -366,22 +366,28 @@ InternalCalculateTscFrequency (
> InterruptState = SaveAndDisableInterrupts ();
>
> TimerAddr = InternalAcpiGetAcpiTimerIoPort ();
> - Ticks = IoRead32 (TimerAddr) + (ACPI_TIMER_FREQUENCY / 10000); // Set Ticks to
> 100us in the future
> + //
> + // Compute the number of ticks to wait to measure TSC frequency.
> + // Use 363 * 9861 = 3579543 Hz which is within 2 Hz of ACPI_TIMER_FREQUENCY.
> + // 363 counts is a calibration time of 101.4 uS.
> + //
> + Ticks = IoRead32 (TimerAddr) + 363;
>
> StartTSC = AsmReadTsc (); // Get base
> value for the TSC
> //
> - // Wait until the ACPI timer has counted 100us.
> + // Wait until the ACPI timer has counted 101.4 us.
> // Timer wrap-arounds are handled correctly by this function.
> - // When the current ACPI timer value is greater than 'Ticks', the while loop will
> exit.
> + // When the current ACPI timer value is greater than 'Ticks',
> + // the while loop will exit.
> //
> while (((Ticks - IoRead32 (TimerAddr)) & BIT23) == 0) {
> CpuPause();
> }
> - EndTSC = AsmReadTsc (); // TSC value
> 100us later
> + EndTSC = AsmReadTsc (); // TSC value
> 101.4 us later
>
> TscFrequency = MultU64x32 (
> - (EndTSC - StartTSC), // Number of TSC
> counts in 100us
> - 10000 // Number of
> 100us in a second
> + (EndTSC - StartTSC), // Number of TSC
> counts in 101.4 us
> + 9861 // Number of
> 101.4 us in a second
> );
>
> SetInterruptState (InterruptState);
> diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
> b/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
> index 8819ebcfccef..29521f8b220b 100644
> --- a/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
> +++ b/PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.c
> @@ -20,13 +20,13 @@
> Calculate TSC frequency.
>
> The TSC counting frequency is determined by comparing how far it counts
> - during a 100us period as determined by the ACPI timer. The ACPI timer is
> - used because it counts at a known frequency.
> - The TSC is sampled, followed by waiting for ACPI_TIMER_FREQUENCY / 10000
> - clocks of the ACPI timer, or 100us. The TSC is then sampled again. The
> - difference multiplied by 10000 is the TSC frequency. There will be a small
> - error because of the overhead of reading the ACPI timer. An attempt is
> - made to determine and compensate for this error.
> + during a 101.4 us period as determined by the ACPI timer.
> + The ACPI timer is used because it counts at a known frequency.
> + The TSC is sampled, followed by waiting 363 counts of the ACPI timer,
> + or 101.4 us. The TSC is then sampled again. The difference multiplied by
> + 9861 is the TSC frequency. There will be a small error because of the
> + overhead of reading the ACPI timer. An attempt is made to determine and
> + compensate for this error.
>
> @return The number of TSC counts per second.
>
> diff --git a/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c
> b/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c
> index 7f7b0f8f6294..b141c680fb82 100644
> --- a/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c
> +++ b/PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.c
> @@ -20,13 +20,13 @@
> Calculate TSC frequency.
>
> The TSC counting frequency is determined by comparing how far it counts
> - during a 100us period as determined by the ACPI timer. The ACPI timer is
> - used because it counts at a known frequency.
> - The TSC is sampled, followed by waiting for ACPI_TIMER_FREQUENCY / 10000
> - clocks of the ACPI timer, or 100us. The TSC is then sampled again. The
> - difference multiplied by 10000 is the TSC frequency. There will be a small
> - error because of the overhead of reading the ACPI timer. An attempt is
> - made to determine and compensate for this error.
> + during a 101.4 us period as determined by the ACPI timer.
> + The ACPI timer is used because it counts at a known frequency.
> + The TSC is sampled, followed by waiting 363 counts of the ACPI timer,
> + or 101.4 us. The TSC is then sampled again. The difference multiplied by
> + 9861 is the TSC frequency. There will be a small error because of the
> + overhead of reading the ACPI timer. An attempt is made to determine and
> + compensate for this error.
>
> @return The number of TSC counts per second.
>
> --
> 2.7.0.windows.1
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2016-08-17 15:49 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2016-08-17 2:26 [PATCH] PcAtChipsetPkg AcpiTimerLib: Wait 363 ACPI timer counts to get TSC Freq Star Zeng
2016-08-17 10:31 ` Paolo Bonzini
2016-08-17 15:47 ` Kinney, Michael D
2016-08-17 15:49 ` Kinney, Michael D
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