Messages in this thread Patch in this message | | | From | David Ahern <> | Subject | [PATCH] perf record: mmap output file - v2 | Date | Mon, 14 Oct 2013 20:55:31 -0600 |
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When recording raw_syscalls for the entire system, e.g., perf record -e raw_syscalls:*,sched:sched_switch -a -- sleep 1
you end up with a negative feedback loop as perf itself calls write() fairly often. This patch handles the problem by mmap'ing the file in chunks of 64M at a time and copies events from the event buffers to the file avoiding write system calls.
Before (with write syscall):
perf record -o /tmp/perf.data -e raw_syscalls:*,sched:sched_switch -a -- sleep 1 [ perf record: Woken up 0 times to write data ] [ perf record: Captured and wrote 81.843 MB /tmp/perf.data (~3575786 samples) ]
After (using mmap):
perf record -o /tmp/perf.data -e raw_syscalls:*,sched:sched_switch -a -- sleep 1 [ perf record: Woken up 31 times to write data ] [ perf record: Captured and wrote 8.203 MB /tmp/perf.data (~358388 samples) ]
In addition to perf-trace benefits using mmap lowers the overhead of perf-record. For example,
perf stat -i -- perf record -g -o /tmp/perf.data openssl speed aes
showsi a drop in time, CPU cycles, and instructions all drop by more than a factor of 3. Jiri also ran a test that showed a big improvement.
v2: removed msync call before munmap per Jiri's suggestion
Signed-off-by: David Ahern <dsahern@gmail.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Stephane Eranian <eranian@google.com> --- tools/perf/builtin-record.c | 85 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 85 insertions(+)
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c index 92ca5419073b..a1cf20e65089 100644 --- a/tools/perf/builtin-record.c +++ b/tools/perf/builtin-record.c @@ -29,6 +29,9 @@ #include <sched.h> #include <sys/mman.h> +/* mmap file big chunks at a time */ +#define MMAP_OUTPUT_SIZE (64*1024*1024) + #ifndef HAVE_ON_EXIT_SUPPORT #ifndef ATEXIT_MAX #define ATEXIT_MAX 32 @@ -64,6 +67,14 @@ static void __handle_on_exit_funcs(void) struct perf_record { struct perf_tool tool; struct perf_record_opts opts; + + /* for MMAP based file writes */ + void *mmap_addr; + u64 bytes_at_mmap_start; /* bytes in file when mmap use starts */ + u64 mmap_offset; /* current location within mmap */ + size_t mmap_size; /* size of mmap segments */ + bool use_mmap; + u64 bytes_written; const char *output_name; struct perf_evlist *evlist; @@ -82,8 +93,65 @@ static void advance_output(struct perf_record *rec, size_t size) rec->bytes_written += size; } +static int do_mmap_output(struct perf_record *rec, void *buf, size_t size) +{ + u64 remaining; + off_t offset; + + if (rec->mmap_addr == NULL) { +do_mmap: + offset = rec->bytes_at_mmap_start + rec->bytes_written; + if (offset < (ssize_t) rec->mmap_size) { + rec->mmap_offset = offset; + offset = 0; + } else + rec->mmap_offset = 0; + + rec->mmap_addr = mmap(NULL, rec->mmap_size, + PROT_WRITE | PROT_READ, + MAP_SHARED, + rec->output, + offset); + + if (rec->mmap_addr == MAP_FAILED) { + pr_err("mmap failed: %d: %s\n", errno, strerror(errno)); + return -1; + } + + /* expand file to include this mmap segment */ + if (ftruncate(rec->output, offset + rec->mmap_size) != 0) { + pr_err("ftruncate failed\n"); + return -1; + } + } + + remaining = rec->mmap_size - rec->mmap_offset; + + if (size > remaining) { + memcpy(rec->mmap_addr + rec->mmap_offset, buf, remaining); + rec->bytes_written += remaining; + + size -= remaining; + buf += remaining; + + munmap(rec->mmap_addr, rec->mmap_size); + goto do_mmap; + } + + if (size) { + memcpy(rec->mmap_addr + rec->mmap_offset, buf, size); + rec->bytes_written += size; + rec->mmap_offset += size; + } + + return 0; +} + static int write_output(struct perf_record *rec, void *buf, size_t size) { + if (rec->use_mmap) + return do_mmap_output(rec, buf, size); + while (size) { int ret = write(rec->output, buf, size); @@ -546,6 +614,11 @@ static int __cmd_record(struct perf_record *rec, int argc, const char **argv) if (forks) perf_evlist__start_workload(evsel_list); + if (!rec->opts.pipe_output && stat(output_name, &st) == 0) { + rec->use_mmap = true; + rec->bytes_at_mmap_start = st.st_size - rec->bytes_written; + } + for (;;) { int hits = rec->samples; @@ -572,6 +645,17 @@ static int __cmd_record(struct perf_record *rec, int argc, const char **argv) } } + if (rec->use_mmap) { + off_t len = rec->bytes_at_mmap_start + rec->bytes_written; + + rec->use_mmap = false; + munmap(rec->mmap_addr, rec->mmap_size); + rec->mmap_addr = NULL; + + if (ftruncate(rec->output, len) != 0) + pr_err("ftruncate failed\n"); + } + if (quiet || signr == SIGUSR1) return 0; @@ -807,6 +891,7 @@ static struct perf_record record = { .uses_mmap = true, }, }, + .mmap_size = MMAP_OUTPUT_SIZE, }; #define CALLCHAIN_HELP "do call-graph (stack chain/backtrace) recording: " -- 1.7.10.1
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