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Message-ID: <67908fc3-b8a9-4a05-a1ff-2e56be2a6568@amd.com>
Date: Tue, 19 Mar 2024 16:06:40 +0530
From: Sandipan Das <sandipan.das@....com>
To: Ingo Molnar <mingo@...nel.org>
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
x86@...nel.org, peterz@...radead.org, acme@...nel.org, namhyung@...nel.org,
mark.rutland@....com, alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
adrian.hunter@...el.com, tglx@...utronix.de, bp@...en8.de,
seanjc@...gle.com, pbonzini@...hat.com, eranian@...gle.com,
irogers@...gle.com, ravi.bangoria@....com, ananth.narayan@....com
Subject: Re: [PATCH v4 1/2] x86/cpufeatures: Add dedicated feature word for
CPUID leaf 0x80000022[EAX]
On 3/19/2024 3:47 PM, Ingo Molnar wrote:
>
> * Sandipan Das <sandipan.das@....com> wrote:
>
>> Move the existing scattered performance monitoring related feature bits
>> from CPUID leaf 0x80000022[EAX] into a dedicated word since additional
>> bits will be defined from the same leaf in the future. This includes
>> X86_FEATURE_PERFMON_V2 and X86_FEATURE_AMD_LBR_V2.
>>
>> Signed-off-by: Sandipan Das <sandipan.das@....com>
>> ---
>> arch/x86/include/asm/cpufeature.h | 7 +++++--
>> arch/x86/include/asm/cpufeatures.h | 10 +++++++---
>> arch/x86/include/asm/disabled-features.h | 3 ++-
>> arch/x86/include/asm/required-features.h | 3 ++-
>> arch/x86/kernel/cpu/common.c | 3 +++
>> arch/x86/kernel/cpu/scattered.c | 2 --
>> arch/x86/kvm/cpuid.c | 5 +----
>> arch/x86/kvm/reverse_cpuid.h | 1 -
>> 8 files changed, 20 insertions(+), 14 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
>> index a1273698fc43..68dd27d60748 100644
>> --- a/arch/x86/include/asm/cpufeature.h
>> +++ b/arch/x86/include/asm/cpufeature.h
>> @@ -33,6 +33,7 @@ enum cpuid_leafs
>> CPUID_7_EDX,
>> CPUID_8000_001F_EAX,
>> CPUID_8000_0021_EAX,
>> + CPUID_8000_0022_EAX,
>
>> #define X86_FEATURE_SYSCALL32 ( 3*32+14) /* "" syscall in IA32 userspace */
>> #define X86_FEATURE_SYSENTER32 ( 3*32+15) /* "" sysenter in IA32 userspace */
>> #define X86_FEATURE_REP_GOOD ( 3*32+16) /* REP microcode works well */
>> -#define X86_FEATURE_AMD_LBR_V2 ( 3*32+17) /* AMD Last Branch Record Extension Version 2 */
>> +/* FREE! ( 3*32+17) */
>> #define X86_FEATURE_CLEAR_CPU_BUF ( 3*32+18) /* "" Clear CPU buffers using VERW */
>> #define X86_FEATURE_ACC_POWER ( 3*32+19) /* AMD Accumulated Power Mechanism */
>> #define X86_FEATURE_NOPL ( 3*32+20) /* The NOPL (0F 1F) instructions */
>> @@ -209,7 +209,7 @@
>> #define X86_FEATURE_SSBD ( 7*32+17) /* Speculative Store Bypass Disable */
>> #define X86_FEATURE_MBA ( 7*32+18) /* Memory Bandwidth Allocation */
>> #define X86_FEATURE_RSB_CTXSW ( 7*32+19) /* "" Fill RSB on context switches */
>> -#define X86_FEATURE_PERFMON_V2 ( 7*32+20) /* AMD Performance Monitoring Version 2 */
>> +/* FREE! ( 7*32+20) */
>> #define X86_FEATURE_USE_IBPB ( 7*32+21) /* "" Indirect Branch Prediction Barrier enabled */
>> #define X86_FEATURE_USE_IBRS_FW ( 7*32+22) /* "" Use IBRS during runtime firmware calls */
>> #define X86_FEATURE_SPEC_STORE_BYPASS_DISABLE ( 7*32+23) /* "" Disable Speculative Store Bypass. */
>> @@ -459,6 +459,10 @@
>> #define X86_FEATURE_IBPB_BRTYPE (20*32+28) /* "" MSR_PRED_CMD[IBPB] flushes all branch type predictions */
>> #define X86_FEATURE_SRSO_NO (20*32+29) /* "" CPU is not affected by SRSO */
>>
>> +/* AMD-defined performance monitoring features, CPUID level 0x80000022 (EAX), word 21 */
>> +#define X86_FEATURE_PERFMON_V2 (21*32+ 0) /* AMD Performance Monitoring Version 2 */
>> +#define X86_FEATURE_AMD_LBR_V2 (21*32+ 1) /* AMD Last Branch Record Extension Version 2 */
>
> Thank you! I presume you tested both patches on the relevant system
> with the X86_FEATURE_AMD_LBR_PMC_FREEZE bug?
>
Yes, I tested them on systems which don't support freeze.
When kernel branches are captured on such systems, the records mostly
point to amd_pmu_lbr_read() and native_read_msr() which are called to
read the branch record MSRs. This is the expected result since LBR
does not stop recording branches after a PMC overflow.
E.g.
# To display the perf.data header info, please use --header/--header-only options.
#
#
# Total Lost Samples: 0
#
# Samples: 190K of event 'ex_ret_brn_tkn'
# Event count (approx.): 190144
#
# Overhead Command Source Shared Object Source Symbol Target Symbol Basic Block Cycles
# ........ ....... .................... ........................... ........................... ..................
#
24.98% branchy [kernel.kallsyms] [k] amd_pmu_lbr_read [k] amd_pmu_lbr_read -
12.49% branchy [kernel.kallsyms] [k] amd_pmu_lbr_read [k] native_read_msr -
12.49% branchy [kernel.kallsyms] [k] native_read_msr [k] native_read_msr -
12.49% branchy [kernel.kallsyms] [k] srso_alias_safe_ret [k] amd_pmu_lbr_read -
12.49% branchy [kernel.kallsyms] [k] srso_alias_safe_ret [k] srso_alias_safe_ret -
12.49% branchy [kernel.kallsyms] [k] srso_alias_return_thunk [k] srso_alias_return_thunk -
6.25% branchy [kernel.kallsyms] [k] native_read_msr [k] srso_alias_return_thunk -
6.25% branchy [kernel.kallsyms] [k] srso_alias_return_thunk [k] srso_alias_safe_ret -
0.02% perf-ex [kernel.kallsyms] [k] amd_pmu_lbr_read [k] amd_pmu_lbr_read -
0.01% perf-ex [kernel.kallsyms] [k] amd_pmu_lbr_read [k] native_read_msr -
0.01% perf-ex [kernel.kallsyms] [k] native_read_msr [k] native_read_msr -
0.01% perf-ex [kernel.kallsyms] [k] srso_alias_safe_ret [k] amd_pmu_lbr_read -
0.01% perf-ex [kernel.kallsyms] [k] srso_alias_safe_ret [k] srso_alias_safe_ret -
0.01% perf-ex [kernel.kallsyms] [k] srso_alias_return_thunk [k] srso_alias_return_thunk -
0.00% perf-ex [kernel.kallsyms] [k] native_read_msr [k] srso_alias_return_thunk -
0.00% perf-ex [kernel.kallsyms] [k] srso_alias_return_thunk [k] srso_alias_safe_ret -
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