Re: [RFC PATCH 00/10] perf: add workqueue library and use it in synthetic-events

[Arnaldo Carvalho de Melo]

Em Tue, Jul 13, 2021 at 02:11:11PM +0200, Riccardo Mancini escreveu:
> This patchset introduces a new utility library inside perf/util, which
> provides a work queue abstraction, which loosely follows the Kernel
> workqueue API.
> 
> The workqueue abstraction is made up by two components:
>  - threadpool: which takes care of managing a pool of threads. It is
>    inspired by the prototype for threaded trace in perf-record from Alexey:
>    https://lore.kernel.org/lkml/cover.1625227739.git.alexey.v.bayduraev@xxxxxxxxxxxxxxx/
>  - workqueue: manages a shared queue and provides the workers implementation.
> 
> On top of the workqueue, a simple parallel-for utility is implemented
> which is then showcased in synthetic-events.c, replacing the previous
> manual pthread-created threads.
> 
> Through some experiments with perf bench, I can see how the new 
> workqueue has a higher overhead compared to manual creation of threads, 
> but is able to more effectively partition work among threads, yielding 
> a better result with more threads.
> Furthermore, the overhead could be configured by changing the
> `work_size` (currently 1), aka the number of dirents that are 
> processed by a thread before grabbing a lock to get the new work item.
> I experimented with different sizes but, while bigger sizes reduce overhead
> as expected, they do not scale as well to more threads.
> 
> I tried to keep the patchset as simple as possible, deferring possible
> improvements and features to future work.
> Naming a few:
>  - in order to achieve a better performance, we could consider using 
>    work-stealing instead of a common queue.
>  - affinities in the thread pool, as in Alexey prototype for
>    perf-record. Doing so would enable reusing the same threadpool for
>    different purposes (evlist open, threaded trace, synthetic threads),
>    avoiding having to spin up threads multiple times.
>  - resizable threadpool, e.g. for lazy spawining of threads.
> 
> @Arnaldo
> Since I wanted the workqueue to provide a similar API to the Kernel's
> workqueue, I followed the naming style I found there, instead of the
> usual object__method style that is typically found in perf. 
> Let me know if you'd like me to follow perf style instead.

You did the right thing, that is how we do with other kernel APIs, we
use list_add(), rb_first(), bitmap_weight(), hash_del(),  etc.

- Arnaldo
 
> Thanks,
> Riccardo
> 
> Riccardo Mancini (10):
>   perf workqueue: threadpool creation and destruction
>   perf tests: add test for workqueue
>   perf workqueue: add threadpool start and stop functions
>   perf workqueue: add threadpool execute and wait functions
>   perf workqueue: add sparse annotation header
>   perf workqueue: introduce workqueue struct
>   perf workqueue: implement worker thread and management
>   perf workqueue: add queue_work and flush_workqueue functions
>   perf workqueue: add utility to execute a for loop in parallel
>   perf synthetic-events: use workqueue parallel_for
> 
>  tools/perf/tests/Build                 |   1 +
>  tools/perf/tests/builtin-test.c        |   9 +
>  tools/perf/tests/tests.h               |   3 +
>  tools/perf/tests/workqueue.c           | 453 +++++++++++++++++
>  tools/perf/util/Build                  |   1 +
>  tools/perf/util/synthetic-events.c     | 131 +++--
>  tools/perf/util/workqueue/Build        |   2 +
>  tools/perf/util/workqueue/sparse.h     |  21 +
>  tools/perf/util/workqueue/threadpool.c | 516 ++++++++++++++++++++
>  tools/perf/util/workqueue/threadpool.h |  29 ++
>  tools/perf/util/workqueue/workqueue.c  | 642 +++++++++++++++++++++++++
>  tools/perf/util/workqueue/workqueue.h  |  38 ++
>  12 files changed, 1771 insertions(+), 75 deletions(-)
>  create mode 100644 tools/perf/tests/workqueue.c
>  create mode 100644 tools/perf/util/workqueue/Build
>  create mode 100644 tools/perf/util/workqueue/sparse.h
>  create mode 100644 tools/perf/util/workqueue/threadpool.c
>  create mode 100644 tools/perf/util/workqueue/threadpool.h
>  create mode 100644 tools/perf/util/workqueue/workqueue.c
>  create mode 100644 tools/perf/util/workqueue/workqueue.h
> 
> -- 
> 2.31.1
> 

-- 

- Arnaldo