Re: [PATCH v12 2/3]: perf record: enable asynchronous trace writing

[Jiri Olsa]

On Tue, Oct 09, 2018 at 11:58:53AM +0300, Alexey Budankov wrote:
> 
> Trace file offset is read once before mmaps iterating loop and written
> back after all performance data enqueued for aio writing. Trace file offset 
> is incremented linearly after every successful aio write operation. 
> 
> record__aio_sync() blocks till completion of started AIO operation 
> and then proceeds.
> 
> record__mmap_read_sync() implements a barrier for all incomplete
> aio write requests.
> 
> Signed-off-by: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx>
> ---
>  Changes in v12:
>  - implemented record__aio_get/set_pos(), record__aio_enabled()
>  - implemented simple --aio option
>  Changes in v11:
>  - replacing the both lseek() syscalls in every loop iteration by the only 
>    two syscalls just before and after the loop at record__mmap_read_evlist() 
>    and advancing *in-flight* off file pos value at perf_mmap__aio_push()
>  Changes in v10:
>  - avoided lseek() setting file pos back in case of record__aio_write() failure
>  - compacted code selecting between serial and AIO streaming
>  - optimized call places of record__mmap_read_sync()
>  Changes in v9:
>  - enable AIO streaming only when --aio-cblocks option is specified explicitly
>  Changes in v8:
>  - split AIO completion check into separate record__aio_complete()
>  Changes in v6:
>  - handled errno == EAGAIN case from aio_write();
>  Changes in v5:
>  - data loss metrics decreased from 25% to 2x in trialed configuration;
>  - avoided nanosleep() prior calling aio_suspend();
>  - switched to per cpu multi record__aio_sync() aio
>  - record_mmap_read_sync() now does global barrier just before 
>    switching trace file or collection stop;
>  - resolved livelock on perf record -e intel_pt// -- dd if=/dev/zero of=/dev/null count=100000
>  Changes in v4:
>  - converted void *bf to struct perf_mmap *md in signatures
>  - written comment in perf_mmap__push() just before perf_mmap__get();
>  - written comment in record__mmap_read_sync() on possible restarting 
>    of aio_write() operation and releasing perf_mmap object after all;
>  - added perf_mmap__put() for the cases of failed aio_write();
>  Changes in v3:
>  - written comments about nanosleep(0.5ms) call prior aio_suspend()
>    to cope with intrusiveness of its implementation in glibc;
>  - written comments about rationale behind coping profiling data 
>    into mmap->data buffer;
> ---
>  tools/perf/Documentation/perf-record.txt |   5 +
>  tools/perf/builtin-record.c              | 220 ++++++++++++++++++++++++++++++-
>  tools/perf/perf.h                        |   1 +
>  tools/perf/util/evlist.c                 |   6 +-
>  tools/perf/util/evlist.h                 |   2 +-
>  tools/perf/util/mmap.c                   |  86 +++++++++++-
>  tools/perf/util/mmap.h                   |   5 +
>  7 files changed, 316 insertions(+), 9 deletions(-)
> 
> diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
> index 246dee081efd..5cedb3e75434 100644
> --- a/tools/perf/Documentation/perf-record.txt
> +++ b/tools/perf/Documentation/perf-record.txt
> @@ -435,6 +435,11 @@ Specify vmlinux path which has debuginfo.
>  --buildid-all::
>  Record build-id of all DSOs regardless whether it's actually hit or not.
>  
> +--aio::
> +Enable asynchronous (Posix AIO) trace writing mode. 

nit, there's an extra whitespace at the end of above line,
making the 'git am' to not apply your patch

thanks,
jirka