Commit c1afca10 authored by Dapeng Mi's avatar Dapeng Mi Committed by Arnaldo Carvalho de Melo
Browse files

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

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: cf8e55fe ("KVM: x86/pmu: Expose CPUIDs feature bits PDCM, DS, DTES64")
Reported-by: default avatarKevin Tian <kevin.tian@intel.com>
Signed-off-by: default avatarDapeng Mi <dapeng1.mi@linux.intel.com>
Acked-by: default avatarNamhyung 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: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 0f53264d

tools/perf/arch/x86/util/kvm-stat.c

+51 −0
Original line number Diff line number Diff line
@@ -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;

}

tools/perf/builtin-kvm.c

+0 −10
Original line number Diff line number Diff line
@@ -1636,16 +1636,6 @@ static int kvm_events_report_vcpu(struct perf_kvm_stat *kvm) 
	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;

tools/perf/util/kvm-stat.h

+10 −0
Original line number Diff line number Diff line
@@ -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 */