Re: [PATCH 03/10] MdeModulePkg/AtaAtapiPassThru: disable the device at ExitBootServices()

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 25 October 2017 at 16:26, Laszlo Ersek <lersek@redhat.com> wrote:
> Hi Star, Eric,
>
> On 09/08/17 00:41, Laszlo Ersek wrote:
>> The AtaAtapiPassThru driver maps three system memory regions for Bus
>> Master Common Buffer operation on the following call path, if the
>> controller has PCI_CLASS_MASS_STORAGE_SATADPA class code:
>>
>>   AtaAtapiPassThruStart()
>>     EnumerateAttachedDevice()
>>       AhciModeInitialization()
>>         AhciCreateTransferDescriptor()
>>
>> The device is disabled (including Bus Master DMA) when the controller is
>> unbound, in AtaAtapiPassThruStop(). Then the regions are unmapped.
>>
>> The former step should also be done when we exit the boot services, and
>> the OS gains ownership of system memory.
>>
>> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> Cc: Brijesh Singh <brijesh.singh@amd.com>
>> Cc: Eric Dong <eric.dong@intel.com>
>> Cc: Jiewen Yao <jiewen.yao@intel.com>
>> Cc: Star Zeng <star.zeng@intel.com>
>> Contributed-under: TianoCore Contribution Agreement 1.1
>> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
>> ---
>>  MdeModulePkg/Bus/Ata/AtaAtapiPassThru/AtaAtapiPassThru.h |  6 ++
>>  MdeModulePkg/Bus/Ata/AtaAtapiPassThru/AtaAtapiPassThru.c | 59 +++++++++++++++++++-
>>  2 files changed, 64 insertions(+), 1 deletion(-)
>
> this patch -- that is, commit 6fb8ddd36bde
> ("MdeModulePkg/AtaAtapiPassThru: disable the device at
> ExitBootServices()", 2017-09-03) -- has caused a performance regression
> in OVMF, in booting Windows installer ISOs from emulated IDE CD-ROMs.
>
> Interestingly, the performance regression only affects the "traditional"
> IDE controller of the "pc" (i440fx) machine type of QEMU; it does not
> affect the AHCI/SATA controller of the "q35" machine type.

Does it make any difference if you only disable memory decoding and
bus mastering, but leave I/O port decoding enabled?