linux-kernel - Re: Large slowdown with 'x86: Avoid invoking RCU when CPU is idle'

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Date:	Fri, 24 Feb 2012 11:27:46 -0500
From:	Josh Boyer <jwboyer@...hat.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, kernel-team@...oraproject.org
Subject: Re: Large slowdown with 'x86: Avoid invoking RCU when CPU is idle'

On Fri, Feb 24, 2012 at 08:17:43AM -0800, Paul E. McKenney wrote:
> On Fri, Feb 24, 2012 at 09:40:32AM -0500, Josh Boyer wrote:
> > On Tue, Feb 21, 2012 at 08:42:43PM -0500, Josh Boyer wrote:
> > > > And patch #47 in that series has been obsoleted by another series
> > > > from Steven Rostedt:
> > > > 
> > > > 	https://lkml.org/lkml/2012/2/7/231
> > > 
> > > Ok.
> > > 
> > > > Hopefully these fix both splats and slowness.
> > > 
> > > So again, I'm slightly confused on how RCU patches flow.  Eric
> > > originally reported the bug for which you created the patch I applied
> > > against 3.3.  The giant patch series above seems queued for 3.4.
> > > 
> > > I don't see stable CC'd on 45-47, nor any of Steven's patches.  I doubt
> > > I'd want to go applying the 47-patch series on 3.3 at the moment, and
> > > given you have these marked for 3.4 I don't think you do either.
> > > However, is there some kind of fix for the original bug report against
> > > 3.3?
> > 
> > I was being sincere when I asked the above questions.  Could you
> > describe how you handle RCU patches across releases and if there is a
> > fix for the 3.3-rcX issue Eric reported that is going into 3.3?
> > 
> > I know you're quite busy, but I'd like to understand your thinking so I
> > know what to expect going forward.
> 
> Apologies for being slow, but could you please point me at the original
> bug report that the old patch was designed to fix?  My email filing
> seems to have failed me in this case.

Same thread I linked in my original email:

https://lkml.org/lkml/2012/1/24/203

> My guess is that the best short-term fix for Fedora is to disable the
> warning, but I do need to see the original bug to work out if that really
> is a prudent course of action.

Honestly, I don't care from a Fedora perspective.  I can do what I need
to do there without too much trouble.  I'm asking because afaik, upstream
still has this problem.  The thread gets a bit curvy but from what I can
tell it resulted in the patch I highlighted as having issues.  Maybe I
overlooked something else that fixed Eric's problem?

josh
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