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

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Date:	Thu, 19 Nov 2015 09:16:02 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Chris Wilson <chris@...is-wilson.co.uk>
Cc:	Chuck Ebbert <cebbert.lkml@...il.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>,
	Andy Lutomirski <luto@...capital.net>,
	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>,
	Daniel Vetter <daniel.vetter@...ll.ch>
Subject: Re: i915.ko WC writes are slow after ea8596bb2d8d379


* Chris Wilson <chris@...is-wilson.co.uk> wrote:

> > > A bisection pointed to 
> > > 
> > > commit ea8596bb2d8d37957f3e92db9511c50801689180
> > > Author: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> > > Date:   Thu Jul 18 20:47:53 2013 +0900
> > > 
> > >     kprobes/x86: Remove unused text_poke_smp() and text_poke_smp_batch() functions
> > > 
> > > of which the active ingredient was just
> > > 
> > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > > index b32ebf9..f4001e0 100644
> > > --- a/arch/x86/Kconfig
> > > +++ b/arch/x86/Kconfig
> > > @@ -2334,7 +2334,6 @@ config HAVE_ATOMIC_IOMAP
> > >  
> > >  config HAVE_TEXT_POKE_SMP
> > >         bool
> > > -       select STOP_MACHINE if SMP

Ouch...

This is certainly an educative example of how pure 'code removal' patches can have 
unintended side effects.

Is there a full fix patch available, and is anyone pushing that to Linus?

Thanks,

	Ingo
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