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* [RFC PATCH v2 00/10] perf: add workqueue library and use it in synthetic-events
@ 2021-07-30 15:34 Riccardo Mancini
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From: Riccardo Mancini @ 2021-07-30 15:34 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo
Cc: Ian Rogers, Namhyung Kim, Peter Zijlstra, Ingo Molnar,
Mark Rutland, Jiri Olsa, linux-kernel, linux-perf-users,
Alexey Bayduraev, Riccardo Mancini
Changes in v2:
- rename threadpool_struct and its functions to adhere to naming style
- use ERR_PTR instead of returning NULL
- add *__strerror functions, removing pr_err from library code
- wait for threads after creation of all threads, instead of waiting
after each creation
- use intention-revealing macros in test code instead of 0 and -1
- use readn/writen functions
This patchset introduces a new utility library inside perf/util, which
provides a work queue abstraction, which loosely follows the Kernel
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:
- 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 slightly higher overhead compared to manual creation of
threads, but is able to more effectively partition work among threads,
yielding better results overall.
Furthermore, the overhead could be reduced 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 believe the next steps are, in order:
- add support to specifying affinities to threads.
- add worker queues with round robin assignment (replacing the current
- optionally add work stealing among the worker queues. I'd keep it a
future work for the moment since we do not have a specific use case
for it at the moment (the synthetic threads would not benefit too
much from it imo).
- add support to executing jobs on a specific worker (which will have
its own affinity). This is useful for Alexey's usecase and for the
following evlist open usecase.
- make workqueue directly manage the threadpool (as Arnaldo already
suggested). We could also make the workqueue global but that requires
an autogrow feature so that threads are created on demand and not all
at the beginning. I'd keep it a future work.
- apply workqueue to the evlist open (the idea is to pin each thread to
a GPU and submit a work_struct for each evsel/cpu to the matching cpu).
Any comment or idea is highly appreciated.
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
tools: add sparse context/locking annotations in compiler-types.h
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/include/linux/compiler_types.h | 18 +
tools/perf/tests/Build | 1 +
tools/perf/tests/builtin-test.c | 9 +
tools/perf/tests/tests.h | 3 +
tools/perf/tests/workqueue.c | 450 +++++++++++++++
tools/perf/util/Build | 1 +
tools/perf/util/synthetic-events.c | 155 ++---
tools/perf/util/workqueue/Build | 2 +
tools/perf/util/workqueue/threadpool.c | 674 ++++++++++++++++++++++
tools/perf/util/workqueue/threadpool.h | 40 ++
tools/perf/util/workqueue/workqueue.c | 750 +++++++++++++++++++++++++
tools/perf/util/workqueue/workqueue.h | 51 ++
12 files changed, 2080 insertions(+), 74 deletions(-)
create mode 100644 tools/perf/tests/workqueue.c
create mode 100644 tools/perf/util/workqueue/Build
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
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