Messages in this thread | | | From | Lai Jiangshan <> | Date | Thu, 19 Nov 2020 09:58:24 +0800 | Subject | Re: workqueue: Only kick a worker after thawed or for an unbound workqueue |
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On Wed, Nov 18, 2020 at 5:05 PM Yunfeng Ye <yeyunfeng@huawei.com> wrote: > > > > On 2020/11/18 14:26, Yunfeng Ye wrote: > > > > > > On 2020/11/18 12:06, Lai Jiangshan wrote: > >> On Tue, Nov 17, 2020 at 3:33 PM Yunfeng Ye <yeyunfeng@huawei.com> wrote: > >>> > >>> In realtime scenario, We do not want to have interference on the > >>> isolated cpu cores. but when invoking alloc_workqueue() for percpu wq > >>> on the housekeeping cpu, it kick a kworker on the isolated cpu. > >>> > >>> alloc_workqueue > >>> pwq_adjust_max_active > >>> wake_up_worker > >>> > >>> The comment in pwq_adjust_max_active() said: > >>> "Need to kick a worker after thawed or an unbound wq's > >>> max_active is bumped" > >>> > >>> So it is unnecessary to kick a kworker for percpu wq's when > >>> alloc_workqueue. this patch only kick a worker after thawed or for an > >>> unbound workqueue. > >>> > >>> Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com> > >>> --- > >>> kernel/workqueue.c | 18 +++++++++++++----- > >>> 1 file changed, 13 insertions(+), 5 deletions(-) > >>> > >>> diff --git a/kernel/workqueue.c b/kernel/workqueue.c > >>> index c41c3c17b86a..80f7bbd4889f 100644 > >>> --- a/kernel/workqueue.c > >>> +++ b/kernel/workqueue.c > >>> @@ -3696,14 +3696,16 @@ static void pwq_unbound_release_workfn(struct work_struct *work) > >>> } > >>> > >>> /** > >>> - * pwq_adjust_max_active - update a pwq's max_active to the current setting > >>> + * pwq_adjust_max_active_and_kick - update a pwq's max_active to the current setting > >>> * @pwq: target pool_workqueue > >>> + * @force_kick: force to kick a worker > >>> * > >>> * If @pwq isn't freezing, set @pwq->max_active to the associated > >>> * workqueue's saved_max_active and activate delayed work items > >>> * accordingly. If @pwq is freezing, clear @pwq->max_active to zero. > >>> */ > >>> -static void pwq_adjust_max_active(struct pool_workqueue *pwq) > >>> +static void pwq_adjust_max_active_and_kick(struct pool_workqueue *pwq, > >>> + bool force_kick) > >>> { > >>> struct workqueue_struct *wq = pwq->wq; > >>> bool freezable = wq->flags & WQ_FREEZABLE; > >>> @@ -3733,9 +3735,10 @@ static void pwq_adjust_max_active(struct pool_workqueue *pwq) > >>> > >>> /* > >>> * Need to kick a worker after thawed or an unbound wq's > >>> - * max_active is bumped. It's a slow path. Do it always. > >>> + * max_active is bumped. > >> > >> > >> Hello > >> > >> Thanks for reporting the problem. > >> > >> But I don't like to add an argument. The waking up is called > >> always just because it was considered no harm and it is slow > >> path. But it can still be possible to detect if the waking up > >> is really needed based on the actual activation of delayed works. > >> > >> The previous lines are: > >> > >> while (!list_empty(&pwq->delayed_works) && > >> pwq->nr_active < pwq->max_active) > >> pwq_activate_first_delayed(pwq); > >> > >> And you can record the old pwq->nr_active before these lines: > >> > >> int old_nr_active = pwq->nr_active; > >> > >> while (!list_empty(&pwq->delayed_works) && > >> pwq->nr_active < pwq->max_active) > >> pwq_activate_first_delayed(pwq); > >> > >> /* please add more comments here, see 951a078a5 */ > >> if (old_nr_active < pwq->nr_active) { > >> if (!old_nr_active || (wq->flags & WQ_UNBOUND)) > >> wake_up_worker(pwq->pool); > >> } > >> > > Ok, I will send a patch v2. > > Thanks. > > > I think it is unnecessary to distinguish the percpu or unbound's wq, > kick a worker always based on the actual activation of delayed works. > > Look like this: > > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > index c41c3c17b86a..cd551dcb2cc9 100644 > --- a/kernel/workqueue.c > +++ b/kernel/workqueue.c > @@ -3725,17 +3725,23 @@ static void pwq_adjust_max_active(struct pool_workqueue *pwq) > * is updated and visible. > */ > if (!freezable || !workqueue_freezing) { > + bool kick = false; > + > pwq->max_active = wq->saved_max_active; > > while (!list_empty(&pwq->delayed_works) && > - pwq->nr_active < pwq->max_active) > + pwq->nr_active < pwq->max_active) { > pwq_activate_first_delayed(pwq); > + kick = true; > + } > > /* > * Need to kick a worker after thawed or an unbound wq's > - * max_active is bumped. It's a slow path. Do it always. > + * max_active is bumped. It's a slow path. Do it always > + * based on the actual activation of delayed works. > */ > - wake_up_worker(pwq->pool); > + if (kick) > + wake_up_worker(pwq->pool); > } else { > pwq->max_active = 0; > } > > Is it OK? > Thanks.
It is OK, since it is a slow path. Please also add comments to the code for reasons not to wake up in some cases as described in your previous comments.
> > >> > >> Thanks for your work. > >> Lai. > >> > >>> */ > >>> - wake_up_worker(pwq->pool); > >>> + if (force_kick || (wq->flags & WQ_UNBOUND)) > >>> + wake_up_worker(pwq->pool); > >>> } else { > >>> pwq->max_active = 0; > >>> } > >>> @@ -3743,6 +3746,11 @@ static void pwq_adjust_max_active(struct pool_workqueue *pwq) > >>> raw_spin_unlock_irqrestore(&pwq->pool->lock, flags); > >>> } > >>> > >>> +static void pwq_adjust_max_active(struct pool_workqueue *pwq) > >>> +{ > >>> + pwq_adjust_max_active_and_kick(pwq, false); > >>> +} > >>> + > >>> /* initialize newly alloced @pwq which is associated with @wq and @pool */ > >>> static void init_pwq(struct pool_workqueue *pwq, struct workqueue_struct *wq, > >>> struct worker_pool *pool) > >>> @@ -5252,7 +5260,7 @@ void thaw_workqueues(void) > >>> list_for_each_entry(wq, &workqueues, list) { > >>> mutex_lock(&wq->mutex); > >>> for_each_pwq(pwq, wq) > >>> - pwq_adjust_max_active(pwq); > >>> + pwq_adjust_max_active_and_kick(pwq, true); > >>> mutex_unlock(&wq->mutex); > >>> } > >>> > >>> -- > >>> 2.18.4 > >> . > >>
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