From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>,
mingo@elte.hu, hpa@zytor.com, trenn@novell.com,
prarit@redhat.com, tj@kernel.org, rusty@rustcorp.com.au,
akpm@linux-foundation.org, torvalds@linux-foundation.org,
linux-kernel@vger.kernel.org, youquan.song@intel.com,
stable@kernel.org
Subject: Re: [patch 1/4] x86, mtrr: lock stop machine during MTRR rendezvous sequence
Date: Thu, 23 Jun 2011 11:33:16 +0200 (CEST) [thread overview]
Message-ID: <alpine.LFD.2.02.1106231131300.11814@ionos> (raw)
In-Reply-To: <1308819905.1022.70.camel@twins>
On Thu, 23 Jun 2011, Peter Zijlstra wrote:
> On Wed, 2011-06-22 at 15:20 -0700, Suresh Siddha wrote:
> > +#ifdef CONFIG_SMP
> > + /*
> > + * If we are not yet online, then there can be no stop_machine() in
> > + * parallel. Stop machine ensures this by using get_online_cpus().
> > + *
> > + * If we are online, then we need to prevent a stop_machine() happening
> > + * in parallel by taking the stop cpus mutex.
> > + */
> > + if (cpu_online(raw_smp_processor_id()))
> > + mutex_lock(&stop_cpus_mutex);
> > +#endif
>
> This reads like an optimization, is it really worth-while to not take
> the mutex in the rare offline case?
You cannot block on a mutex when you are not online, in fact you
cannot block on it when not active, so the check is wrong anyway.
Thanks,
tglx
next prev parent reply other threads:[~2011-06-23 9:33 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-22 22:20 [patch 0/4] MTRR rendezvous deadlock fix and cleanups using stop_machine() Suresh Siddha
2011-06-22 22:20 ` [patch 1/4] x86, mtrr: lock stop machine during MTRR rendezvous sequence Suresh Siddha
2011-06-23 9:05 ` Peter Zijlstra
2011-06-23 9:33 ` Thomas Gleixner [this message]
2011-06-23 9:41 ` Peter Zijlstra
2011-06-23 18:16 ` Suresh Siddha
2011-06-22 22:20 ` [patch 2/4] stop_machine: reorganize stop_cpus() implementation Suresh Siddha
2011-06-22 22:20 ` [patch 3/4] stop_machine: implement stop_machine_from_offline_cpu() Suresh Siddha
2011-06-23 9:25 ` Peter Zijlstra
2011-06-23 9:28 ` Tejun Heo
2011-06-23 9:31 ` Peter Zijlstra
2011-06-23 18:19 ` Suresh Siddha
2011-06-24 7:45 ` Peter Zijlstra
2011-06-24 17:55 ` Suresh Siddha
2011-06-22 22:20 ` [patch 4/4] x86, mtrr: use stop_machine() for doing MTRR rendezvous Suresh Siddha
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