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Message-Id: <20250805004633.135904-5-dapeng1.mi@linux.intel.com>
Date: Tue, 5 Aug 2025 08:46:32 +0800
From: Dapeng Mi <dapeng1.mi@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Kan Liang <kan.liang@...ux.intel.com>
Cc: linux-perf-users@...r.kernel.org,
linux-kernel@...r.kernel.org,
Kevin Tian <kevin.tian@...el.com>,
Dapeng Mi <dapeng1.mi@...el.com>,
Dapeng Mi <dapeng1.mi@...ux.intel.com>
Subject: [PATCH 4/5] 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) ]
Reported-by: Kevin Tian <kevin.tian@...el.com>
Fixes: 634d36f82517 ("perf record: Just use "cycles:P" as the default event")
Signed-off-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
---
tools/perf/arch/x86/util/kvm-stat.c | 46 +++++++++++++++++++++++++++++
1 file changed, 46 insertions(+)
diff --git a/tools/perf/arch/x86/util/kvm-stat.c b/tools/perf/arch/x86/util/kvm-stat.c
index 424716518b75..cdb5f3e1b5be 100644
--- a/tools/perf/arch/x86/util/kvm-stat.c
+++ b/tools/perf/arch/x86/util/kvm-stat.c
@@ -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 +213,47 @@ 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 i, j = *argc;
+
+ const struct option event_options[] = {
+ OPT_BOOLEAN('e', "event", &event, NULL),
+ OPT_END()
+ };
+
+ if (!x86__is_intel_cpu())
+ return 0;
+
+ tmp = calloc(j + 1, sizeof(char *));
+ if (!tmp)
+ return -EINVAL;
+
+ 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("-e");
+ argv[j++] = strdup("cycles");
+ *argc += 2;
+ }
+
+ free(tmp);
+ return 0;
+}
--
2.34.1
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