Messages in this thread | | | Subject | Re: [PATCH v9 2/3]: perf record: enable asynchronous trace writing | From | Alexey Budankov <> | Date | Fri, 5 Oct 2018 11:31:11 +0300 |
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Hi,
On 05.10.2018 10:16, Namhyung Kim wrote: > On Wed, Oct 03, 2018 at 07:12:10PM +0300, Alexey Budankov wrote: <SNIP> >> +static void record__aio_sync(struct perf_mmap *md) >> +{ >> + struct aiocb *cblock = &md->cblock; >> + struct timespec timeout = { 0, 1000 * 1000 * 1 }; // 1ms >> + >> + do { >> + if (cblock->aio_fildes == -1 || record__aio_complete(md, cblock)) >> + return; >> + >> + while (aio_suspend((const struct aiocb**)&cblock, 1, &timeout)) { >> + if (!(errno == EAGAIN || errno == EINTR)) >> + pr_err("failed to sync perf data, error: %m\n"); > > Is there somthing we can do in this error case? Any chance it gets > stuck in the loop?
Not really. Currently, in glibc, it can block on a mutex only.
> > >> + } >> + } while (1); >> +} >> + >> +static int record__aio_pushfn(void *to, struct aiocb *cblock, void *bf, size_t size) >> +{ >> + off_t off; >> + struct record *rec = to; >> + int ret, trace_fd = rec->session->data->file.fd; >> + >> + rec->samples++; >> + >> + off = lseek(trace_fd, 0, SEEK_CUR); >> + lseek(trace_fd, off + size, SEEK_SET); > > It'd be nice if these lseek() could be removed and use > rec->bytes_written instead.
Well, this could be implemented like this avoiding lseek() in else branch:
off = lseek(trace_fd, 0, SEEK_CUR); ret = record__aio_write(cblock, trace_fd, bf, size, off); if (!ret) { lseek(trace_fd, off + size, SEEK_SET); rec->bytes_written += size;
if (switch_output_size(rec)) trigger_hit(&switch_output_trigger); } > > >> + ret = record__aio_write(cblock, trace_fd, bf, size, off); >> + if (!ret) { >> + rec->bytes_written += size; >> + >> + if (switch_output_size(rec)) >> + trigger_hit(&switch_output_trigger); > > Doesn't it need the _sync() before the trigger? Maybe it should be > moved to record__mmap_read_evlist() or so..
Currently trigger just updates variable state. The state is then checked thru separate API at __cmd_record() where record__mmap_read_sync() is called prior switching to a new trace file or finishing collection.
>> <SNIP> >> if (map->base) { >> +#ifndef HAVE_AIO_SUPPORT >> if (perf_mmap__push(map, rec, record__pushfn) != 0) { >> rc = -1; >> goto out; >> } >> +#else >> + if (!rec->opts.nr_cblocks) { >> + if (perf_mmap__push(map, rec, record__pushfn) != 0) { >> + rc = -1; >> + goto out; >> + } >> + } else { >> + /* >> + * Call record__aio_sync() to wait till map->data buffer >> + * becomes available after previous aio write request. >> + */ >> + record__aio_sync(map); >> + if (perf_mmap__aio_push(map, rec, record__aio_pushfn) != 0) { >> + rc = -1; >> + goto out; >> + } >> + } >> +#endif > > If dummy aio functions are provided, the #ifdef can be removed and > just use the #else part assuming opts.nr_cblocks == 0.
Yes, it looks a little bit cumbersome. Would this be more compact?
if (map->base) { #ifdef HAVE_AIO_SUPPORT if (!rec->opts.nr_cblocks) { #endif if (perf_mmap__push(map, rec, record__pushfn) != 0) { rc = -1; goto out; } #ifdef HAVE_AIO_SUPPORT } else { int idx; /* * Call record__aio_sync() to wait till map->data buffer * becomes available after previous aio write request. */ idx = record__aio_sync(map, false); if (perf_mmap__aio_push(map, rec, idx, record__aio_pushfn) != 0) { rc = -1; goto out; } } #endif }
Thanks, Alexey
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