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perf tools kvm: Use "cycles" to sample guest for "kvm record" on Intel

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After KVM supports PEBS for guest on Intel platforms
(https://lore.kernel.org/all/20220411101946.20262-1-likexu@tencent.com/),
host loses the capability to sample guest with PEBS since all PEBS related
MSRs are switched to guest value after vm-entry, like IA32_DS_AREA MSR is
switched to guest GVA at vm-entry. This would lead to "perf kvm record"
fails to sample guest on Intel platforms since "cycles:P" event is used to
sample guest by default as below case shows.

sudo perf kvm record -a
^C[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.787 MB perf.data.guest ]

So to ensure guest record can be sampled successfully, use "cycles"
instead of "cycles:P" to sample guest record by default on Intel
platforms. With this patch, the guest record can be sampled
successfully.

sudo perf kvm record -a
^C[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.783 MB perf.data.guest (23 samples) ]

Fixes: cf8e55fe50 ("KVM: x86/pmu: Expose CPUIDs feature bits PDCM, DS, DTES64")
Reported-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Like Xu <likexu@tencent.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Dapeng Mi
2025-09-19 10:16:58 +08:00
committed by Arnaldo Carvalho de Melo
parent 0f53264d71
commit c1afca106e
3 changed files with 61 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

51
tools/perf/arch/x86/util/kvm-stat.c
View File

@@ -3,9 +3,11 @@
#include <string.h>
#include "../../../util/kvm-stat.h"
#include "../../../util/evsel.h"
#include "../../../util/env.h"
#include <asm/svm.h>
#include <asm/vmx.h>
#include <asm/kvm.h>
#include <subcmd/parse-options.h>
define_exit_reasons_table(vmx_exit_reasons, VMX_EXIT_REASONS);
define_exit_reasons_table(svm_exit_reasons, SVM_EXIT_REASONS);
@@ -211,3 +213,52 @@ int cpu_isa_init(struct perf_kvm_stat *kvm, const char *cpuid)
return 0;
}
/*
* After KVM supports PEBS for guest on Intel platforms
* (https://lore.kernel.org/all/20220411101946.20262-1-likexu@tencent.com/),
* host loses the capability to sample guest with PEBS since all PEBS related
* MSRs are switched to guest value after vm-entry, like IA32_DS_AREA MSR is
* switched to guest GVA at vm-entry. This would lead to "perf kvm record"
* fails to sample guest on Intel platforms since "cycles:P" event is used to
* sample guest by default.
*
* So, to avoid this issue explicitly use "cycles" instead of "cycles:P" event
* by default to sample guest on Intel platforms.
*/
int kvm_add_default_arch_event(int *argc, const char **argv)
{
const char **tmp;
bool event = false;
int ret = 0, i, j = *argc;
const struct option event_options[] = {
OPT_BOOLEAN('e', "event", &event, NULL),
OPT_BOOLEAN(0, "pfm-events", &event, NULL),
OPT_END()
};
if (!x86__is_intel_cpu())
return 0;
tmp = calloc(j + 1, sizeof(char *));
if (!tmp)
return -ENOMEM;
for (i = 0; i < j; i++)
tmp[i] = argv[i];
parse_options(j, tmp, event_options, NULL, PARSE_OPT_KEEP_UNKNOWN);
if (!event) {
argv[j++] = STRDUP_FAIL_EXIT("-e");
argv[j++] = STRDUP_FAIL_EXIT("cycles");
*argc += 2;
}
free(tmp);
return 0;
EXIT:
free(tmp);
return ret;
}

10
tools/perf/builtin-kvm.c
View File

@@ -1636,16 +1636,6 @@ exit:
return ret;
}
#define STRDUP_FAIL_EXIT(s) \
({ char *_p; \
_p = strdup(s); \
if (!_p) { \
ret = -ENOMEM; \
goto EXIT; \
} \
_p; \
})
int __weak setup_kvm_events_tp(struct perf_kvm_stat *kvm __maybe_unused)
{
return 0;

10
tools/perf/util/kvm-stat.h
View File

@@ -190,5 +190,15 @@ static inline struct kvm_info *kvm_info__new(void)
#define kvm_info__zput(ki) do { } while (0)
#endif /* HAVE_KVM_STAT_SUPPORT */
#define STRDUP_FAIL_EXIT(s) \
({ char *_p; \
_p = strdup(s); \
if (!_p) { \
ret = -ENOMEM; \
goto EXIT; \
} \
_p; \
})
extern int kvm_add_default_arch_event(int *argc, const char **argv);
#endif /* __PERF_KVM_STAT_H */