From: "Laszlo Ersek" <lersek@redhat.com>
To: edk2-devel-groups-io <devel@edk2.groups.io>
Cc: Eric Dong <eric.dong@intel.com>, Ray Ni <ray.ni@intel.com>
Subject: [PATCH v2 1/2] UefiCpuPkg/MpInitLib: expand comment on initial AP enumeration
Date: Thu, 10 Oct 2019 13:29:51 +0200 [thread overview]
Message-ID: <20191010112952.7187-2-lersek@redhat.com> (raw)
In-Reply-To: <20191010112952.7187-1-lersek@redhat.com>
Before adding another AP enumeration mode, clarify the documentation on
the current logic. No functional changes.
Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1515
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
---
Notes:
v2:
- new patch
UefiCpuPkg/Library/MpInitLib/MpLib.c | 38 +++++++++++++++-----
1 file changed, 30 insertions(+), 8 deletions(-)
diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c b/UefiCpuPkg/Library/MpInitLib/MpLib.c
index d6f84c6f45c0..594a035d8b92 100644
--- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
+++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
@@ -1045,14 +1045,36 @@ WakeUpAP (
}
if (CpuMpData->InitFlag == ApInitConfig) {
//
- // Here support two methods to collect AP count through adjust
- // PcdCpuApInitTimeOutInMicroSeconds values.
- //
- // one way is set a value to just let the first AP to start the
- // initialization, then through the later while loop to wait all Aps
- // finsh the initialization.
- // The other way is set a value to let all APs finished the initialzation.
- // In this case, the later while loop is useless.
+ // The AP enumeration algorithm below is suitable for two use cases.
+ //
+ // (1) The check-in time for an individual AP is bounded, and APs run
+ // through their initialization routines strongly concurrently. In
+ // particular, the number of concurrently running APs
+ // ("NumApsExecuting") is never expected to fall to zero
+ // *temporarily* -- it is expected to fall to zero only when all
+ // APs have checked-in.
+ //
+ // In this case, the platform is supposed to set
+ // PcdCpuApInitTimeOutInMicroSeconds to a low-ish value (just long
+ // enough for one AP to start initialization). The timeout will be
+ // reached soon, and remaining APs are collected by watching
+ // NumApsExecuting fall to zero. If NumApsExecuting falls to zero
+ // mid-process, while some APs have not completed initialization,
+ // the behavior is undefined.
+ //
+ // (2) The check-in time for an individual AP is unbounded, and/or APs
+ // may complete their initializations widely spread out. In
+ // particular, some APs may finish initialization before some APs
+ // even start.
+ //
+ // In this case, the platform is supposed to set
+ // PcdCpuApInitTimeOutInMicroSeconds to a high-ish value. The AP
+ // enumeration will always take that long (except when the boot CPU
+ // count happens to be maximal, that is,
+ // PcdCpuMaxLogicalProcessorNumber). All APs are expected to
+ // check-in before the timeout, and NumApsExecuting is assumed zero
+ // at timeout. APs that miss the time-out may cause undefined
+ // behavior.
//
TimedWaitForApFinish (
CpuMpData,
--
2.19.1.3.g30247aa5d201
next prev parent reply other threads:[~2019-10-10 11:29 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-10 11:29 [PATCH v2 0/2] UefiCpuPkg/MpInitLib: introduce PcdCpuBootLogicalProcessorNumber Laszlo Ersek
2019-10-10 11:29 ` Laszlo Ersek [this message]
2019-10-11 8:19 ` [PATCH v2 1/2] UefiCpuPkg/MpInitLib: expand comment on initial AP enumeration Ni, Ray
2019-10-10 11:29 ` [PATCH v2 2/2] UefiCpuPkg/MpInitLib: honor the platform's boot CPU count in AP detection Laszlo Ersek
2019-10-11 8:22 ` Ni, Ray
2019-10-11 21:31 ` [edk2-devel] " Laszlo Ersek
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