Messages in this thread | | | Subject | Re: [PATCH v1 2/2]: perf record: enable asynchronous trace writing | From | Alexey Budankov <> | Date | Mon, 27 Aug 2018 12:20:50 +0300 |
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Hi,
On 27.08.2018 0:48, Jiri Olsa wrote: > On Tue, Aug 21, 2018 at 11:27:03AM +0300, Alexey Budankov wrote: > > SNIP > >> -static int record__pushfn(void *to, void *bf, size_t size) >> +static int record__pushfn(void *to, void *bf, size_t size, off_t off) >> { >> struct record *rec = to; >> + struct perf_mmap *map = bf; >> >> rec->samples++; >> - return record__write(rec, bf, size); >> + return record__aio_write(rec->session->data->file.fd, &map->cblock, >> + map->data, size, off); >> } >> >> static volatile int done; >> @@ -528,13 +530,85 @@ static struct perf_event_header finished_round_event = { >> .type = PERF_RECORD_FINISHED_ROUND, >> }; >> >> +static int record__mmap_read_sync(int trace_fd, struct aiocb **cblocks, >> + int cblocks_size, struct record *rec) >> +{ >> + size_t rem; >> + ssize_t size; >> + off_t rem_off; >> + int i, aio_ret, aio_errno, do_suspend; >> + struct perf_mmap *md; >> + struct timespec timeout0 = { 0, 0 }; >> + struct timespec timeoutS = { 0, 1000 * 500 * 1 }; >> + >> + if (!cblocks_size) >> + return 0; >> + >> + do { >> + do_suspend = 0; >> + nanosleep(&timeoutS, NULL); > > why the extra sleep in here and not sleeping through aio_suspend call?
Yep. Good question. That requires explicit explanation:
+ /* aio_suspend() implementation inside glibc (as of v2.27) is + * intrusive and not just blocks waiting io requests completion + * but polls requests queue inducing context switches in perf + * tool process. When profiling in system wide mode with tracing + * context switches the trace may be polluted by context switches + * from the perf process and the trace size becomes about 3-5 + * times bigger than that of when writing the trace serially. + * To limit the volume of context switches from perf tool + * process nonsleep() call limits aio_suspend() + * polling till every half of the kernel timer tick which is + * usually 1ms (depends on CONFIG_HZ value). + */
> > jirka > >> + if (aio_suspend((const struct aiocb**)cblocks, cblocks_size, &timeout0)) { >> + if (errno == EAGAIN || errno == EINTR) { >> + do_suspend = 1; >> + continue; >> + } else { >> + pr_err("failed to sync perf data, error: %m\n"); > > SNIP >
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