From: Ingo Molnar <mingo@elte.hu>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Nick Piggin <npiggin@suse.de>, Jens Axboe <jens.axboe@oracle.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Rusty Russell <rusty@rustcorp.com.au>,
linux-kernel@vger.kernel.org, Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH 1.5/2] generic-smp: fix initial quiesent count.
Date: Sun, 15 Feb 2009 00:29:41 +0100 [thread overview]
Message-ID: <20090214232941.GI20477@elte.hu> (raw)
In-Reply-To: <1234646056.4695.10.camel@laptop>
* Peter Zijlstra <peterz@infradead.org> wrote:
> On Sat, 2009-02-14 at 15:46 +0100, Peter Zijlstra wrote:
> > first compile, then send out...
> >
> > ---
> > Subject: generic-smp: fix initial quiesent count.
> > From: Peter Zijlstra <a.p.zijlstra@chello.nl>
> > Date: Sat Feb 14 15:36:07 CET 2009
> >
> > If we start with a quiesent sequence count of 0, we'll match the initial stamp
> > values of the cfd_data, and never make any progress.
> >
> > To avoid getting stuck in this situation, start out with an increased quiesent
> > sequence count.
>
> OK, so this is not going to fix the problem in generic. Its still
> possible to end up with the original issue.
>
> We'd need a callback list to free used entries, much like regular RCU,
> this quiesent sequence count's wrapping just seems too brittle.
Ok, given that your series was hanging on a number of testboxes here,
lets go with my original simplification?
The broadcasting-to-a-lot-of-CPUs case is going to suck on any seriously
large system no matter what. It's single-IPI and few-IPI performance that
matters mostly.
Ingo
next prev parent reply other threads:[~2009-02-14 23:32 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-02-12 22:32 [PATCH 0/2] generic smp helpers vs kmalloc Peter Zijlstra
2009-02-12 22:32 ` [PATCH 1/2] generic-smp: remove single ipi fallback for smp_call_function_many() Peter Zijlstra
2009-02-14 14:41 ` [PATCH 1.5/2] generic-smp: fix initial quiesent count Peter Zijlstra
2009-02-14 14:46 ` Peter Zijlstra
2009-02-14 21:14 ` Peter Zijlstra
2009-02-14 23:29 ` Ingo Molnar [this message]
2009-02-12 22:32 ` [PATCH 2/2] generic-smp: remove kmalloc usage Peter Zijlstra
2009-02-14 14:46 ` [PATCH 2.5/2] generic-smp: remove cfd rcu_head Peter Zijlstra
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