[PATCH 2/2] x86/cpu/amd: Enable the fixed intructions retired free counter IRPERF

Kim Phillips
2020-01-15T20:57:19Z

commit aaf248848db50 ("perf/x86/msr: Add AMD IRPERF (Instructions
Retired) performance counter") added support for 'perf -e msr/irperf/',
but when exercised, we always get a 0 count:

BEFORE:

$ sudo perf stat -e instructions,msr/irperf/ true

Performance counter stats for 'true':

624,833 instructions
# 0.00 stalled cycles per insn
0 msr/irperf/

It turns out it simply needs its enable bit - HWCR bit 30 - set. This patch
does just that.

Enablement is restricted to all machines advertising IRPERF capability,
except those susceptible to an erratum that makes the IRPERF return
bad values.

That erratum occurs in Family 17h models 00-1fh [1], but not in F17h
models 20h and above [2].

AFTER (on a family 17h model 31h machine):

$ sudo perf stat -e instructions,msr/irperf/ true

Performance counter stats for 'true':

621,690 instructions
# 0.00 stalled cycles per insn
622,490 msr/irperf/

[1] "Revision Guide for AMD Family 17h Models 00h-0Fh Processors",
currently available here:

https://www.amd.com/system/files/TechDocs/55449_Fam_17h_M_00h-0Fh_Rev_Guide.pdf

[2] "Revision Guide for AMD Family 17h Models 30h-3Fh Processors",
currently available here:

https://developer.amd.com/wp-content/resources/56323-PUB_0.74.pdf

Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Babu Moger <babu.moger@amd.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Frank van der Linden <fllinden@amazon.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Huang Rui <ray.huang@amd.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luwei Kang <luwei.kang@intel.com>
Cc: Martin Liška <mliska@suse.cz>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org
Fixes: aaf248848db50 ("perf/x86/msr: Add AMD IRPERF (Instructions Retired) performance counter")
Signed-off-by: Kim Phillips <kim.phillips@amd.com>
---
arch/x86/include/asm/msr-index.h | 2 ++
arch/x86/kernel/cpu/amd.c | 9 +++++++++
2 files changed, 11 insertions(+)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 084e98da04a7..717660f82f8f 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -512,6 +512,8 @@
#define MSR_K7_HWCR 0xc0010015
#define MSR_K7_HWCR_SMMLOCK_BIT 0
#define MSR_K7_HWCR_SMMLOCK BIT_ULL(MSR_K7_HWCR_SMMLOCK_BIT)
+#define MSR_K7_HWCR_IRPERF_EN_BIT 30
+#define MSR_K7_HWCR_IRPERF_EN BIT_ULL(MSR_K7_HWCR_IRPERF_EN_BIT)
#define MSR_K7_FID_VID_CTL 0xc0010041
#define MSR_K7_FID_VID_STATUS 0xc0010042

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 90f75e515876..765b2b6672eb 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -978,6 +978,15 @@ static void init_amd(struct cpuinfo_x86 *c)
/* AMD CPUs don't reset SS attributes on SYSRET, Xen does. */
if (!cpu_has(c, X86_FEATURE_XENPV))
set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
+
+ /*
+ * Turn on the Instructions Retired free counter on machines not
+ * susceptible to erratum #1054 "Instructions Retired Performance
+ * Counter May Be Inaccurate"
+ */
+ if (cpu_has(c, X86_FEATURE_IRPERF) &&
+ !(c->x86 == 0x17 && c->x86_model <= 0x1f))
+ msr_set_bit(MSR_K7_HWCR, MSR_K7_HWCR_IRPERF_EN_BIT);
}

#ifdef CONFIG_X86_32
--
2.24.1