Date: Thu, 19 Nov 2015 09:16:02 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Chuck Ebbert <cebbert.lkml@gmail.com>, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>, Tejun Heo <tj@kernel.org>,
        Andy Lutomirski <luto@amacapital.net>,
        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: <20151119081602.GC16214@gmail.com>
References: <20141008090336.GD12897@nuc-i3427.alporthouse.com>
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 <20151118144811.GA1043@nuc-i3427.alporthouse.com>
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* Chris Wilson <chris@chris-wilson.co.uk> wrote:

> > > A bisection pointed to 
> > > 
> > > commit ea8596bb2d8d37957f3e92db9511c50801689180
> > > Author: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.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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