Reviewed-by: Ray Ni <ray...@intel.com> > -----Original Message----- > From: Laszlo Ersek <ler...@redhat.com> > Sent: Thursday, October 10, 2019 7:30 PM > To: edk2-devel-groups-io <devel@edk2.groups.io> > Cc: Dong, Eric <eric.d...@intel.com>; Ni, Ray <ray...@intel.com> > Subject: [PATCH v2 1/2] UefiCpuPkg/MpInitLib: expand comment on initial > AP enumeration > > 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 (#48805): https://edk2.groups.io/g/devel/message/48805 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] -=-=-=-=-=-=-=-=-=-=-=-
