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

[Alexey Budankov]

On 11.10.2018 17:15, Jiri Olsa wrote:
> 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

Corrected trailing whitespace. Thanks!

- Alexey

> 
> thanks,
> jirka
>