From: Oleg Nesterov <oleg@tv-sign.ru>
To: paulmck@us.ibm.com
Cc: linux-kernel@vger.kernel.org,
Dipankar Sarma <dipankar@in.ibm.com>,
Manfred Spraul <manfred@colorfullife.com>,
Linus Torvalds <torvalds@osdl.org>, Andrew Morton <akpm@osdl.org>
Subject: Re: [PATCH 2/5] rcu: don't check ->donelist in __rcu_pending()
Date: Mon, 09 Jan 2006 23:31:20 +0300 [thread overview]
Message-ID: <43C2C818.65238C30@tv-sign.ru> (raw)
In-Reply-To: 20060109185944.GB15083@us.ibm.com
"Paul E. McKenney" wrote:
>
> On Sun, Jan 08, 2006 at 10:19:24PM +0300, Oleg Nesterov wrote:
> > ->donelist becomes != NULL only in rcu_process_callbacks().
> >
> > rcu_process_callbacks() always calls rcu_do_batch() when
> > ->donelist != NULL.
> >
> > rcu_do_batch() schedules rcu_process_callbacks() again if
> > ->donelist was not flushed entirely.
> >
> > So ->donelist != NULL means that rcu_tasklet is either
> > TASKLET_STATE_SCHED or TASKLET_STATE_RUN, we don't need to
> > check it in __rcu_pending().
>
> As Vatsa noted, this is needed if the CPU-hotplug case moves
> from ->donelist to ->donelist. It could be omitted if CPU-hotplug
> instead moves from ->donelist to ->nextlist, as is the case in Oleg's
> patch. The extra grace-period delay should not be a problem for the
> presumably rare hotplug case, but:
Just to be sure. So do you agree that CPU-hotplug is buggy now (without
that patch) ?
> o the extra test in __rcu_pending() should be quite inexpensive,
> since the cacheline is already loaded given the earlier tests.
Yes, it was a cleanup, not an optimization.
> o although tasklet_schedule() looks to be perfectly reliable
> right now, and although any bugs in tasklet_schedule() must
> be fixed, having RCU leakage be the major symptom of
> tasklet_schedule() failure sounds quite unfriendly to me.
>
> So I am not (yet) convinced that this patch is the way to go.
Ok, I agree.
Oleg.
next prev parent reply other threads:[~2006-01-09 19:15 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-08 19:19 [PATCH 2/5] rcu: don't check ->donelist in __rcu_pending() Oleg Nesterov
2006-01-08 22:00 ` Paul E. McKenney
2006-01-09 9:31 ` Srivatsa Vaddagiri
2006-01-09 14:51 ` Oleg Nesterov
2006-01-09 13:42 ` Srivatsa Vaddagiri
2006-01-09 15:33 ` Oleg Nesterov
2006-01-09 18:59 ` Paul E. McKenney
2006-01-09 20:31 ` Oleg Nesterov [this message]
2006-01-09 19:59 ` Paul E. McKenney
2006-01-10 9:58 ` Srivatsa Vaddagiri
2006-01-10 14:24 ` [PATCH] rcu: fix hotplug-cpu ->donelist leak Oleg Nesterov
2006-01-11 5:01 ` Paul E. McKenney
2006-01-11 16:28 ` Paul E. McKenney
2006-01-11 19:25 ` Oleg Nesterov
2006-01-11 18:21 ` Paul E. McKenney
2006-01-10 14:27 ` [PATCH 2/5] rcu: don't check ->donelist in __rcu_pending() Oleg Nesterov
2006-01-10 18:13 ` Dipankar Sarma
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