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| author | Laszlo Ersek <lersek@redhat.com> | 2019-10-10 11:07:39 +0200 |
|---|---|---|
| committer | Laszlo Ersek <lersek@redhat.com> | 2019-10-11 23:19:41 +0200 |
| commit | 30459ddde672b3130d7775fe16d91e63c6f95943 (patch) | |
| tree | 265957d60698f97ef8805f788bfd02a3e898e991 /UefiCpuPkg/Library | |
| parent | a7e2d20193e853020a1415c25b53280955055394 (diff) | |
| download | edk2-30459ddde672b3130d7775fe16d91e63c6f95943.tar.gz edk2-30459ddde672b3130d7775fe16d91e63c6f95943.tar.bz2 edk2-30459ddde672b3130d7775fe16d91e63c6f95943.zip | |
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.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>
Reviewed-by: Ray Ni <ray.ni@intel.com>
Diffstat (limited to 'UefiCpuPkg/Library')
| -rw-r--r-- | UefiCpuPkg/Library/MpInitLib/MpLib.c | 36 |
1 files changed, 29 insertions, 7 deletions
diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c b/UefiCpuPkg/Library/MpInitLib/MpLib.c index d6f84c6f45..594a035d8b 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.
+ // The AP enumeration algorithm below is suitable for two use cases.
//
- // 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.
+ // (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,
|