Before adding another AP enumeration mode, clarify the documentation on the current logic. No functional changes.
Cc: Eric Dong <eric.d...@intel.com> Cc: Ray Ni <ray...@intel.com> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1515 Signed-off-by: Laszlo Ersek <ler...@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 -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#48723): https://edk2.groups.io/g/devel/message/48723 Mute This Topic: https://groups.io/mt/34473662/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
