linux-kernel - Re: i915.ko WC writes are slow after ea8596bb2d8d379

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Message-ID: <CALCETrWs2vzFWOFs8vV98OfJTa2=BOwGapuKgsrE7ci8whMgHg@mail.gmail.com>
Date:	Wed, 18 Nov 2015 07:57:35 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Chris Wilson <chris@...is-wilson.co.uk>
Cc:	Chuck Ebbert <cebbert.lkml@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Peter Zijlstra <peterz@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Jiri Kosina <jkosina@...e.cz>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Jason Baron <jbaron@...mai.com>, yrl.pp-manager.tt@...achi.com,
	Borislav Petkov <bpetkov@...e.de>,
	Ingo Molnar <mingo@...nel.org>,
	Daniel Vetter <daniel.vetter@...ll.ch>
Subject: Re: i915.ko WC writes are slow after ea8596bb2d8d379

On Wed, Nov 18, 2015 at 6:48 AM, Chris Wilson <chris@...is-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.

--Andy
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