[RFC PATCH] perf/kvm: Guest Symbol Resolution for powerpc
Hemant Kumar
hemant at linux.vnet.ibm.com
Tue Jun 16 12:50:53 AEST 2015
"perf kvm {record|report}" is used to record and report the performance
profile of any workload on a guest. From the host, we can collect
guest kernel statistics which is useful in finding out any contentions
in guest kernel symbols for a certain workload.
This feature is not available on powerpc because "perf" relies on the
"cycles" event (a PMU event) to profile the guest. However, for powerpc,
this can't be used from the host because the PMUs are controlled by the
guest rather than the host.
Due to this problem, we need a different approach to profile the
workload in the guest. There exists a tracepoint "kvm_hv:kvm_guest_exit"
in powerpc which is hit whenever any of the threads exit the guest
context. The guest instruction pointer dumped along with this
tracepoint data in the field "pc", can be used as guest instruction
pointer while postprocessing the trace data to map this IP to symbol
from guest.kallsyms.
However, to have some kind of periodicity, we can't use all the kvm
exits, rather exits which are bound to happen in certain intervals.
HV_DECREMENTER Interrupt forces the threads to exit after an interval
of 10 ms.
This patch makes use of the "kvm_guest_exit" tracepoint and checks the
exit reason for any kvm exit. If it is HV_DECREMENTER, then the
instruction pointer dumped along with this tracepoint is retrieved and
mapped with the guest kallsyms.
This patch is a prototype asking for suggestions/comments as to whether
the approach is right or is there any way better than this (like using
a different event to profile for, etc) to profile the guest from the
host.
Thank You.
Signed-off-by: Hemant Kumar <hemant at linux.vnet.ibm.com>
---
tools/perf/arch/powerpc/Makefile | 1 +
tools/perf/arch/powerpc/util/parse-tp.c | 55 +++++++++++++++++++++++++++++++++
tools/perf/builtin-report.c | 9 ++++++
tools/perf/util/event.c | 7 ++++-
tools/perf/util/evsel.c | 7 +++++
tools/perf/util/evsel.h | 4 +++
tools/perf/util/session.c | 7 +++--
7 files changed, 86 insertions(+), 4 deletions(-)
create mode 100644 tools/perf/arch/powerpc/util/parse-tp.c
diff --git a/tools/perf/arch/powerpc/Makefile b/tools/perf/arch/powerpc/Makefile
index 6f7782b..992a0d5 100644
--- a/tools/perf/arch/powerpc/Makefile
+++ b/tools/perf/arch/powerpc/Makefile
@@ -4,3 +4,4 @@ LIB_OBJS += $(OUTPUT)arch/$(ARCH)/util/dwarf-regs.o
LIB_OBJS += $(OUTPUT)arch/$(ARCH)/util/skip-callchain-idx.o
endif
LIB_OBJS += $(OUTPUT)arch/$(ARCH)/util/header.o
+LIB_OBJS += $(OUTPUT)arch/$(ARCH)/util/parse-tp.o
diff --git a/tools/perf/arch/powerpc/util/parse-tp.c b/tools/perf/arch/powerpc/util/parse-tp.c
new file mode 100644
index 0000000..4c6e49c
--- /dev/null
+++ b/tools/perf/arch/powerpc/util/parse-tp.c
@@ -0,0 +1,55 @@
+#include "../../util/evsel.h"
+#include "../../util/trace-event.h"
+#include "../../util/session.h"
+
+#define KVMPPC_EXIT "kvm_hv:kvm_guest_exit"
+#define HV_DECREMENTER 2432
+#define HV_BIT 3
+#define PR_BIT 49
+#define PPC_MAX 63
+
+/*
+ * Get the instruction pointer from the tracepoint data
+ */
+u64 arch__get_ip(struct perf_evsel *evsel, struct perf_sample *data)
+{
+ u64 tp_ip = data->ip;
+ int trap;
+
+ if (!strcmp(KVMPPC_EXIT, evsel->name)) {
+ trap = raw_field_value(evsel->tp_format, "trap", data->raw_data);
+
+ if (trap == HV_DECREMENTER)
+ tp_ip = raw_field_value(evsel->tp_format, "pc",
+ data->raw_data);
+ }
+ return tp_ip;
+}
+
+/*
+ * Get the HV and PR bits and accordingly, determine the cpumode
+ */
+u8 arch__get_cpumode(union perf_event *event, struct perf_evsel *evsel,
+ struct perf_sample *data)
+{
+ unsigned long hv, pr, msr;
+ u8 cpumode = event->header.misc & PERF_RECORD_MISC_CPUMODE_MASK;
+
+ if (strcmp(KVMPPC_EXIT, evsel->name))
+ goto ret;
+
+ if (data->raw_data)
+ msr = raw_field_value(evsel->tp_format, "msr", data->raw_data);
+ else
+ goto ret;
+
+ hv = msr & ((long unsigned)1 << (PPC_MAX - HV_BIT));
+ pr = msr & ((long unsigned)1 << (PPC_MAX - PR_BIT));
+
+ if (!hv && pr)
+ cpumode = PERF_RECORD_MISC_GUEST_USER;
+ else
+ cpumode = PERF_RECORD_MISC_GUEST_KERNEL;
+ret:
+ return cpumode;
+}
diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
index 072ae8a..e3fe5d0 100644
--- a/tools/perf/builtin-report.c
+++ b/tools/perf/builtin-report.c
@@ -141,6 +141,13 @@ out:
return err;
}
+u8 __weak arch__get_cpumode(union perf_event *event,
+ __maybe_unused struct perf_evsel *evsel,
+ __maybe_unused struct perf_sample *sample)
+{
+ return event->header.misc & PERF_RECORD_MISC_CPUMODE_MASK;
+}
+
static int process_sample_event(struct perf_tool *tool,
union perf_event *event,
struct perf_sample *sample,
@@ -155,6 +162,8 @@ static int process_sample_event(struct perf_tool *tool,
};
int ret;
+ al.cpumode = arch__get_cpumode(event, evsel, sample);
+
if (perf_event__preprocess_sample(event, machine, &al, sample) < 0) {
pr_debug("problem processing %d event, skipping it.\n",
event->header.type);
diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index 6c6d044..693e37c 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -824,9 +824,14 @@ int perf_event__preprocess_sample(const union perf_event *event,
struct addr_location *al,
struct perf_sample *sample)
{
- u8 cpumode = event->header.misc & PERF_RECORD_MISC_CPUMODE_MASK;
struct thread *thread = machine__findnew_thread(machine, sample->pid,
sample->tid);
+ u8 cpumode;
+
+ if (al->cpumode != PERF_RECORD_MISC_CPUMODE_UNKNOWN)
+ cpumode = al->cpumode;
+ else
+ cpumode = event->header.misc & PERF_RECORD_MISC_CPUMODE_MASK;
if (thread == NULL)
return -1;
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 1e90c85..aa4dd49 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1281,6 +1281,12 @@ static inline bool overflow(const void *endp, u16 max_size, const void *offset,
#define OVERFLOW_CHECK_u64(offset) \
OVERFLOW_CHECK(offset, sizeof(u64), sizeof(u64))
+u64 __weak arch__get_ip(__maybe_unused struct perf_evsel *evsel,
+ __maybe_unused struct perf_sample *data)
+{
+ return data->ip;
+}
+
int perf_evsel__parse_sample(struct perf_evsel *evsel, union perf_event *event,
struct perf_sample *data)
{
@@ -1454,6 +1460,7 @@ int perf_evsel__parse_sample(struct perf_evsel *evsel, union perf_event *event,
OVERFLOW_CHECK(array, data->raw_size, max_size);
data->raw_data = (void *)array;
array = (void *)array + data->raw_size;
+ data->ip = arch__get_ip(evsel, data);
}
if (type & PERF_SAMPLE_BRANCH_STACK) {
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 3862274..5c94d64 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -355,4 +355,8 @@ for ((_evsel) = list_entry((_leader)->node.next, struct perf_evsel, node); \
(_evsel) && (_evsel)->leader == (_leader); \
(_evsel) = list_entry((_evsel)->node.next, struct perf_evsel, node))
+u64 arch__get_ip(struct perf_evsel *evsel, struct perf_sample *data);
+u8 arch__get_cpumode(union perf_event *event, struct perf_evsel *evsel,
+ struct perf_sample *sample);
+
#endif /* __PERF_EVSEL_H */
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 5f0e05a..49698cc 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -748,9 +748,10 @@ static void dump_sample(struct perf_evsel *evsel, union perf_event *event,
static struct machine *
perf_session__find_machine_for_cpumode(struct perf_session *session,
union perf_event *event,
- struct perf_sample *sample)
+ struct perf_sample *sample,
+ struct perf_evsel *evsel)
{
- const u8 cpumode = event->header.misc & PERF_RECORD_MISC_CPUMODE_MASK;
+ u8 cpumode = arch__get_cpumode(event, evsel, sample);
struct machine *machine;
if (perf_guest &&
@@ -856,7 +857,7 @@ int perf_session__deliver_event(struct perf_session *session,
evsel = perf_evlist__id2evsel(session->evlist, sample->id);
machine = perf_session__find_machine_for_cpumode(session, event,
- sample);
+ sample, evsel);
switch (event->header.type) {
case PERF_RECORD_SAMPLE:
--
1.9.3
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