Re: [PATCH 1/2] UefiCpuPkg/MpInitLib: force flushing TLB for AP in mwait loop mode

["Ni, Ruiyu" <ruiyu.ni@Intel.com>]

On 1/26/2018 5:03 PM, Jian J Wang wrote:
> The reason doing this is that we found that calling StartupAllAps() to
> flush TLB for all APs in CpuDxe driver after changing page attributes
> will spend a lot of time to complete. If there are many page attributes
> update requests, the whole system performance will be slowed down
> explicitly, including any shell command and UI operation.
> 
> The solution is removing the flush operation for AP in CpuDxe driver.
> Since TLB is always flushed in HLT loop mode, we just need to enforce
> a TLB flush for mwait loop mode.
> 
> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
> ---
>   UefiCpuPkg/Library/MpInitLib/MpLib.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> index 6231968c74..175a4b49e5 100644
> --- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
> +++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> @@ -630,6 +630,12 @@ ApWakeupFunction (
>           // Restore AP's volatile registers saved
>           //
>           RestoreVolatileRegisters (&CpuMpData->CpuData[ProcessorNumber].VolatileRegisters, TRUE);
> +      } else {
> +        //
> +        // Due to performance concern, the CPU driver might not flush TLB for
> +        // APs on spot. AP itself needs to take care of it when woken up.
> +        //
> +        CpuFlushTlb ();
>         }
>   
>         if (GetApState (&CpuMpData->CpuData[ProcessorNumber]) == CpuStateReady) {
> 
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>

-- 
Thanks,
Ray