On Thu, May 12, 2022 at 04:58:18PM -0700, Paul E. McKenney wrote:
> On Thu, May 12, 2022 at 03:04:30AM +0000, Joel Fernandes (Google) wrote:
> > This will be used in kfree_rcu() later to make it do call_rcu() lazily.
>
> Given that kfree_rcu() does its own laziness in filling in the page
> of pointers, do we really need to add additional laziness?
>
> Or are you measuring a significant benefit from doing this?
The benefit I was measuring was, prior to this, I was seeing frequent calls
to queue_delay_rcu(). Based on the latest test results, though, I am not
seeing a signficant benefit and Vlad also confirms it. So I might drop this
patch completely. For easier testing though, it would be nice to make
KFREE_DRAIN_JIFFIES and mainline that change as well, since I believe we can
achieve similar effect by just increasing that timeout.
thanks!
- Joel
>
> Thanx, Paul
>
> > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> > ---
> > include/linux/workqueue.h | 1 +
> > kernel/workqueue.c | 25 +++++++++++++++++++++++++
> > 2 files changed, 26 insertions(+)
> >
> > diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
> > index 7fee9b6cfede..2678a6b5b3f3 100644
> > --- a/include/linux/workqueue.h
> > +++ b/include/linux/workqueue.h
> > @@ -444,6 +444,7 @@ extern bool queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
> > extern bool mod_delayed_work_on(int cpu, struct workqueue_struct *wq,
> > struct delayed_work *dwork, unsigned long delay);
> > extern bool queue_rcu_work(struct workqueue_struct *wq, struct rcu_work *rwork);
> > +extern bool queue_rcu_work_lazy(struct workqueue_struct *wq, struct rcu_work *rwork);
> >
> > extern void flush_workqueue(struct workqueue_struct *wq);
> > extern void drain_workqueue(struct workqueue_struct *wq);
> > diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> > index 33f1106b4f99..9444949cc148 100644
> > --- a/kernel/workqueue.c
> > +++ b/kernel/workqueue.c
> > @@ -1796,6 +1796,31 @@ bool queue_rcu_work(struct workqueue_struct *wq, struct rcu_work *rwork)
> > }
> > EXPORT_SYMBOL(queue_rcu_work);
> >
> > +/**
> > + * queue_rcu_work_lazy - queue work after a RCU grace period
> > + * @wq: workqueue to use
> > + * @rwork: work to queue
> > + *
> > + * Return: %false if @rwork was already pending, %true otherwise. Note
> > + * that a full RCU grace period is guaranteed only after a %true return.
> > + * While @rwork is guaranteed to be executed after a %false return, the
> > + * execution may happen before a full RCU grace period has passed.
> > + */
> > +bool queue_rcu_work_lazy(struct workqueue_struct *wq, struct rcu_work *rwork)
> > +{
> > + struct work_struct *work = &rwork->work;
> > +
> > + if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
> > + rwork->wq = wq;
> > + call_rcu_lazy(&rwork->rcu, rcu_work_rcufn);
> > + return true;
> > + }
> > +
> > + return false;
> > +}
> > +EXPORT_SYMBOL(queue_rcu_work_lazy);
> > +
> > +
> > /**
> > * worker_enter_idle - enter idle state
> > * @worker: worker which is entering idle state
> > --
> > 2.36.0.550.gb090851708-goog
> >
