Messages in this thread | | | Date | Fri, 24 Feb 2012 08:51:30 -0800 | From | "Paul E. McKenney" <> | Subject | Re: Large slowdown with 'x86: Avoid invoking RCU when CPU is idle' |
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On Fri, Feb 24, 2012 at 11:27:46AM -0500, Josh Boyer wrote: > 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
Thank you!
> > 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?
"A bit curvy" is right -- which is why the fixes ended up at the end of my large patch series for 3.4.
But after looking this over, Steven Rostedt's three-patch set should suffice:
https://lkml.org/lkml/2012/2/7/231
The reason that mine are not needed is that the problematic code is called -only- from idle, not from process context, and also that the problematic code is tracing. My patch #45 is required for code that is called from both process context and from idle. My patch #46 is required for non-tracing uses of RCU from within the idle loop -- along with TBD patches to wrap those uses of RCU in the RCU_NONIDLE() macro.
So again, in your particular case of x86's power-tracing features, Steven Rostedt's three-patch series called out above should be all that you need.
I have CCed Steven in case there is some prerequisite to his patch set.
Thanx, Paul
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