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From: Dennis Zhou <dennis@kernel.org>
To: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>,
	Pavel Begunkov <asml.silence@gmail.com>,
	io-uring@vger.kernel.org, linux-kernel@vger.kernel.org,
	Dennis Zhou <dennis@kernel.org>, Christoph Lameter <cl@linux.com>
Subject: Re: [PATCH 1/2] pcpu_ref: add percpu_ref_tryget_many()
Date: Wed, 18 Dec 2019 11:49:55 -0600
Message-ID: <20191218174955.GA14991@dennisz-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <20191218162642.GC2914998@devbig004.ftw2.facebook.com>

On Wed, Dec 18, 2019 at 08:26:42AM -0800, Tejun Heo wrote:
> (cc'ing Dennis and Christoph and quoting whole body)
> 
> Pavel, can you please cc percpu maintainers on related changes?
> 
> The patch looks fine to me.  Please feel free to add my acked-by.
> 
> On Tue, Dec 17, 2019 at 04:42:59PM -0700, Jens Axboe wrote:
> > CC Tejun on this one. Looks fine to me, and matches the put path.
> > 
> > 
> > On 12/17/19 3:28 PM, Pavel Begunkov wrote:
> > > Add percpu_ref_tryget_many(), which works the same way as
> > > percpu_ref_tryget(), but grabs specified number of refs.
> > > 
> > > Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> > > ---
> > >  include/linux/percpu-refcount.h | 24 ++++++++++++++++++++----
> > >  1 file changed, 20 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
> > > index 390031e816dc..19079b62ce31 100644
> > > --- a/include/linux/percpu-refcount.h
> > > +++ b/include/linux/percpu-refcount.h
> > > @@ -210,15 +210,17 @@ static inline void percpu_ref_get(struct percpu_ref *ref)
> > >  }
> > >  
> > >  /**
> > > - * percpu_ref_tryget - try to increment a percpu refcount
> > > + * percpu_ref_tryget_many - try to increment a percpu refcount
> > >   * @ref: percpu_ref to try-get
> > > + * @nr: number of references to get
> > >   *
> > >   * Increment a percpu refcount unless its count already reached zero.
> > >   * Returns %true on success; %false on failure.

Minor nit: would be nice to change this so the two don't have identical
comments. (eg: Increment a percpu refcount by @nr unless...)
> > >   *
> > >   * This function is safe to call as long as @ref is between init and exit.
> > >   */
> > > -static inline bool percpu_ref_tryget(struct percpu_ref *ref)
> > > +static inline bool percpu_ref_tryget_many(struct percpu_ref *ref,
> > > +					  unsigned long nr)
> > >  {
> > >  	unsigned long __percpu *percpu_count;
> > >  	bool ret;
> > > @@ -226,10 +228,10 @@ static inline bool percpu_ref_tryget(struct percpu_ref *ref)
> > >  	rcu_read_lock();
> > >  
> > >  	if (__ref_is_percpu(ref, &percpu_count)) {
> > > -		this_cpu_inc(*percpu_count);
> > > +		this_cpu_add(*percpu_count, nr);
> > >  		ret = true;
> > >  	} else {
> > > -		ret = atomic_long_inc_not_zero(&ref->count);
> > > +		ret = atomic_long_add_unless(&ref->count, nr, 0);
> > >  	}
> > >  
> > >  	rcu_read_unlock();
> > > @@ -237,6 +239,20 @@ static inline bool percpu_ref_tryget(struct percpu_ref *ref)
> > >  	return ret;
> > >  }
> > >  
> > > +/**
> > > + * percpu_ref_tryget - try to increment a percpu refcount
> > > + * @ref: percpu_ref to try-get
> > > + *
> > > + * Increment a percpu refcount unless its count already reached zero.
> > > + * Returns %true on success; %false on failure.
> > > + *
> > > + * This function is safe to call as long as @ref is between init and exit.
> > > + */
> > > +static inline bool percpu_ref_tryget(struct percpu_ref *ref)
> > > +{
> > > +	return percpu_ref_tryget_many(ref, 1);
> > > +}
> > > +
> > >  /**
> > >   * percpu_ref_tryget_live - try to increment a live percpu refcount
> > >   * @ref: percpu_ref to try-get
> > > 
> > 
> > 
> > -- 
> > Jens Axboe
> > 
> 
> -- 
> tejun

Acked-by: Dennis Zhou <dennis@kernel.org>

Thanks,
Dennis

  reply index

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-17 22:28 [PATCH 0/2] optimise ctx's refs grabbing in io_uring Pavel Begunkov
2019-12-17 22:28 ` [PATCH 1/2] pcpu_ref: add percpu_ref_tryget_many() Pavel Begunkov
2019-12-17 23:42   ` Jens Axboe
2019-12-18 16:26     ` Tejun Heo
2019-12-18 17:49       ` Dennis Zhou [this message]
2019-12-21 15:36         ` Pavel Begunkov
2019-12-17 22:28 ` [PATCH 2/2] io_uring: batch getting pcpu references Pavel Begunkov
2019-12-17 23:21   ` Jens Axboe
2019-12-17 23:31     ` Jens Axboe
2019-12-18  9:25       ` Pavel Begunkov
2019-12-18  9:23     ` Pavel Begunkov
2019-12-18  0:02   ` Jens Axboe
2019-12-18 10:41     ` Pavel Begunkov
2019-12-21 16:15   ` [PATCH v2 0/3] optimise ctx's refs grabbing in io_uring Pavel Begunkov
2019-12-21 16:15     ` [PATCH v2 1/3] pcpu_ref: add percpu_ref_tryget_many() Pavel Begunkov
2019-12-21 16:15     ` [PATCH v2 2/3] io_uring: batch getting pcpu references Pavel Begunkov
2019-12-21 16:15     ` [PATCH RFC v2 3/3] io_uring: batch get(ctx->ref) across submits Pavel Begunkov
2019-12-21 16:20       ` Pavel Begunkov
2019-12-21 16:38         ` Jens Axboe
2019-12-21 16:48           ` Pavel Begunkov
2019-12-21 17:01             ` Jens Axboe
2019-12-21 17:26               ` Pavel Begunkov
2019-12-21 20:12       ` [PATCH v3 0/2] optimise ctx's refs grabbing in io_uring Pavel Begunkov
2019-12-21 20:12         ` [PATCH v3 1/2] pcpu_ref: add percpu_ref_tryget_many() Pavel Begunkov
2019-12-21 20:12         ` [PATCH v3 2/2] io_uring: batch getting pcpu references Pavel Begunkov
2019-12-21 21:56           ` Pavel Begunkov
2019-12-28 11:13         ` [PATCH v4 0/2] optimise ctx's refs grabbing in io_uring Pavel Begunkov
2019-12-28 11:13           ` [PATCH v4 1/2] pcpu_ref: add percpu_ref_tryget_many() Pavel Begunkov
2019-12-28 11:13           ` [PATCH v4 2/2] io_uring: batch getting pcpu references Pavel Begunkov
2019-12-28 11:15             ` Pavel Begunkov
2019-12-28 17:03               ` Jens Axboe
2019-12-28 18:37                 ` Pavel Begunkov
2019-12-30  3:33                   ` Brian Gianforcaro
2019-12-30 18:45                     ` Pavel Begunkov

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