Messages in this thread | | | Date | Tue, 5 Sep 2023 09:22:45 -0400 | Subject | Re: [PATCH] perf/x86/uncore: Correct the number of CHAs on EMR | From | "Liang, Kan" <> |
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On 2023-09-04 3:10 p.m., Ingo Molnar wrote: > > * Liang, Kan <kan.liang@linux.intel.com> wrote: > >> >> >> On 2023-09-03 4:40 a.m., Ingo Molnar wrote: >>> >>> * kan.liang@linux.intel.com <kan.liang@linux.intel.com> wrote: >>> >>>> From: Kan Liang <kan.liang@linux.intel.com> >>>> >>>> The MSR UNC_CBO_CONFIG, which was used to detect the number of CHAs on >>>> SPR, is broken on EMR XCC. It always returns 0. >>>> >>>> Roll back to the discovery method, which can give the correct number for >>>> this case. >>>> >>>> Fixes: 38776cc45eb7 ("perf/x86/uncore: Correct the number of CHAs on SPR") >>>> Reported-by: Stephane Eranian <eranian@google.com> >>>> Reported-by: Yunying Sun <yunying.sun@intel.com> >>>> Tested-by: Yunying Sun <yunying.sun@intel.com> >>>> Signed-off-by: Kan Liang <kan.liang@linux.intel.com> >>>> --- >>>> arch/x86/events/intel/uncore_snbep.c | 4 +++- >>>> 1 file changed, 3 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/arch/x86/events/intel/uncore_snbep.c b/arch/x86/events/intel/uncore_snbep.c >>>> index d49e90dc04a4..c41d7d46481c 100644 >>>> --- a/arch/x86/events/intel/uncore_snbep.c >>>> +++ b/arch/x86/events/intel/uncore_snbep.c >>>> @@ -6475,7 +6475,9 @@ void spr_uncore_cpu_init(void) >>>> type = uncore_find_type_by_id(uncore_msr_uncores, UNCORE_SPR_CHA); >>>> if (type) { >>>> rdmsrl(SPR_MSR_UNC_CBO_CONFIG, num_cbo); >>>> - type->num_boxes = num_cbo; >>>> + /* The MSR doesn't work on the EMR XCC. Roll back to the discovery method. */ >>>> + if (num_cbo) >>>> + type->num_boxes = num_cbo; >>> >>> So in the zero case we don't write type->num_boxes and leave it as-is. >>> >>> How does this fall back to the discovery method, is the existing (default?) >>> value of type->num_boxes some special value? >>> >> >> Starts from SPR, the basic uncore PMON information are retrieved from >> the discovery table (resides in an MMIO space populated by BIOS.). It is >> called the discovery method. The existing value of the type->num_boxes >> is from the discovery table. >> >> On some SPR variants, there is a firmware bug. So the value from the >> discovery table is incorrect. We use the value from >> SPR_MSR_UNC_CBO_CONFIG to replace the one from the discovery table. >> 38776cc45eb7 ("perf/x86/uncore: Correct the number of CHAs on SPR") >> >> Unfortunately, the SPR_MSR_UNC_CBO_CONFIG isn't available for the EMR >> XCC (It works well for other EMR variants). But the above firmware bug >> doesn't impact the EMR XCC. So this patch NOT lets the value from the >> SPR_MSR_UNC_CBO_CONFIG replace the existing value from the discovery table. > > Thanks - the comment & changelog should probably reflect this background. >
I will update the comment & changelog and send a V2.
Thanks, Kan
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