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From:   Namhyung Kim <namhyung@kernel.org>
Date:   Tue, 24 Aug 2021 12:40:40 -0700
Message-ID: <CAM9d7ch4RM5rKrYLKrny3yt3ciK87aqzJ8Wt3ze87u9KBHjyXg@mail.gmail.com>
Subject: Re: [RFC PATCH v3 08/15] perf workqueue: add queue_work and
 flush_workqueue functions
To:     Riccardo Mancini <rickyman7@gmail.com>
Cc:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Ian Rogers <irogers@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Jiri Olsa <jolsa@redhat.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-perf-users <linux-perf-users@vger.kernel.org>,
        Alexey Bayduraev <alexey.v.bayduraev@linux.intel.com>
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On Fri, Aug 20, 2021 at 3:54 AM Riccardo Mancini <rickyman7@gmail.com> wrote:
>
> This patch adds functions to queue and wait work_structs, and
> related tests.
>
> When a new work item is added, the workqueue first checks if there
> are threads to wake up. If so, it wakes it up with the given work item,
> otherwise it will pick the next round-robin thread and queue the work
> item to its queue. A thread which completes its queue will go to sleep.
>
> The round-robin mechanism is implemented through the next_worker
> attibute which will point to the next worker to be chosen for queueing.
> When work is assigned to that worker or when the worker goes to sleep,
> the pointer is moved to the next worker in the busy_list, if any.
> When a worker is woken up, it is added in the busy list just before the
> next_worker, so that it will be chosen as last (it's just been assigned
> a work item).

Do we really need this?  I think some of the complexity comes
because of this.  Can we simply put the works in a list in wq
and workers take it out with a lock?  Then the kernel will
distribute the works among the threads for us.

Maybe we can get rid of worker->lock too..

Thanks,
Namhyung