linux-kernel - Re: [PATCH v4 0/4] Reduce synchronize

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Message-ID: <ZbgMWGmG3g-IvOw6@pc636>
Date: Mon, 29 Jan 2024 21:36:40 +0100
From: Uladzislau Rezki <urezki@...il.com>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Uladzislau Rezki <urezki@...il.com>, RCU <rcu@...r.kernel.org>,
	Neeraj upadhyay <Neeraj.Upadhyay@....com>,
	Boqun Feng <boqun.feng@...il.com>, Hillf Danton <hdanton@...a.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>,
	Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [PATCH v4 0/4] Reduce synchronize_rcu() latency(v4)

On Mon, Jan 29, 2024 at 11:43:43AM -0800, Paul E. McKenney wrote:
> On Mon, Jan 29, 2024 at 05:23:01PM +0100, Uladzislau Rezki wrote:
> > On Fri, Jan 26, 2024 at 11:07:18PM -0800, Paul E. McKenney wrote:
> > > On Thu, Jan 04, 2024 at 05:25:06PM +0100, Uladzislau Rezki (Sony) wrote:
> > > > This is a v4 that tends to improve synchronize_rcu() call. To be more
> > > > specific it is about reducing a waiting time(especially worst cases)
> > > > of caller that blocks until a grace period is elapsed. 
> > > > 
> > > > In general, this series separates synchronize_rcu() callers from other
> > > > callbacks. We keep a dedicated an independent queue, thus the processing
> > > > of it starts as soon as grace period is over, so there is no need to wait
> > > > until other callbacks are processed one by one. Please note, a number of
> > > > callbacks can be 10K, 20K, 60K and so on. That is why this series maintain
> > > > a separate track for this call that blocks a context.
> > > 
> > > And before I forget (again), a possible follow-on to this work is to
> > > reduce cond_synchronize_rcu() and cond_synchronize_rcu_full() latency.
> > > Right now, these wait for a full additional grace period (and maybe
> > > more) when the required grace period has not elapsed.  In contrast,
> > > this work might enable waiting only for the needed portion of a grace
> > > period to elapse.
> > > 
> > Thanks. I see it. Probably we also need to move "sync" related
> > functionality out of tree.c file to the sync.c or something similar
> > to that name. IMO. 
> 
> I would prioritize moving the kfree_rcu() code out of tree.c quite
> a ways over moving out the synchronous-wait code.  ;-)
> 
Indeed. But i am not about priority :)

--
Uladzislau Rezki