On Fri, Jul 11, 2014 at 12:01:04AM +0800, Lai Jiangshan wrote:
> maybe_create_worker() has a strong guarantee that there has at least
> one idle worker on return from this function. This guarantee is guaranteed
> via the check and the retrying in this function.
>
> But the caller (worker_thread()) also has the same check and retrying,
> so the guarantee is not really required and the check and the retrying in
> maybe_create_worker() are unnecessary and redundant.
>
> So we remove the guarantee as well as the check and the retrying. The caller
> takes responsibility to retry when needed.
>
> The only trade-off is that the mayday timer will be removed and re-added
> across retrying. Since retrying is expected as rare case, the trade-off
> is acceptible.
>
> Signed-off-by: Lai Jiangshan <[email protected]>
> ---
> kernel/workqueue.c | 49 ++++++++++++++++++-------------------------------
> 1 files changed, 18 insertions(+), 31 deletions(-)
>
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 92f7ea0c..4fdd6d0 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -1875,14 +1875,17 @@ static void pool_mayday_timeout(unsigned long __pool)
> * @pool: pool to create a new worker for
> *
> * Create a new worker for @pool if necessary. @pool is guaranteed to
> - * have at least one idle worker on return from this function. If
> - * creating a new worker takes longer than MAYDAY_INTERVAL, mayday is
> + * make some progresses on return from this function.
Hmmm.... not really.
> + * 1) success to create a new idle worker. Or
Another work item can race and occupy that worker before this worker
regrabs pool->lock, which is safe because
> + * 2) cool down a while after it failed. Or
> + * 3) condition changed (no longer need to create worker) after it failed.
> + * In any case, the caller will recheck the condition and retry when needed,
> + * so this function doesn't need to retry.
the caller checks the condition again but the above 1/2/3 are
confusing at best.
...
> + worker = create_worker(pool);
> + if (worker) {
> + del_timer_sync(&pool->mayday_timer);
> + spin_lock_irq(&pool->lock);
> + start_worker(worker);
> + return;
> + }
>
> + if (need_to_create_worker(pool))
> schedule_timeout_interruptible(CREATE_COOLDOWN);
Ugh, so we're now inserting delay in the inner function and looping
from the outside? That's messy. I'd prefer removing the outer loop
instead.
Thanks.
--
tejun
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