Date: Thu, 19 Nov 2015 09:14:23 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Chris Wilson <chris@chris-wilson.co.uk>,
        Chuck Ebbert <cebbert.lkml@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>, Tejun Heo <tj@kernel.org>,
        Rusty Russell <rusty@rustcorp.com.au>,
        Peter Zijlstra <peterz@infradead.org>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Jiri Kosina <jkosina@suse.cz>, "H. Peter Anvin" <hpa@linux.intel.com>,
        Steven Rostedt <rostedt@goodmis.org>, Jason Baron <jbaron@akamai.com>,
        yrl.pp-manager.tt@hitachi.com, Borislav Petkov <bpetkov@suse.de>,
        Daniel Vetter <daniel.vetter@ffwll.ch>
Subject: Re: i915.ko WC writes are slow after ea8596bb2d8d379
Message-ID: <20151119081423.GB16214@gmail.com>
References: <20141008090336.GD12897@nuc-i3427.alporthouse.com>
 <20141008051059.65566251@as>
 <20151118144811.GA1043@nuc-i3427.alporthouse.com>
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* Andy Lutomirski <luto@amacapital.net> wrote:

> On Wed, Nov 18, 2015 at 6:48 AM, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> > Although
> >
> > diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h
> > index d2abbdb..ff4f029 100644
> > --- a/include/linux/stop_machine.h
> > +++ b/include/linux/stop_machine.h
> > @@ -97,7 +97,7 @@ static inline int try_stop_cpus(const struct cpumask *cpumask,
> >   * grabbing every spinlock (and more).  So the "read" side to such a
> >   * lock is anything which disables preemption.
> >   */
> > -#if defined(CONFIG_STOP_MACHINE) && defined(CONFIG_SMP)
> > +#if defined(CONFIG_SMP) || defined(CONFIG_HOTPLUG_CPU)
> 
> [...]
> 
> This seems much better.  Having a set of stop_machine functions around
> that don't work depending on config seems dangerous.

Agreed.

Acked-by: Ingo Molnar <mingo@kernel.org>

Thanks,

	Ingo
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