linux-kernel - Re: [PATCH] arm/perf: Fix pmu percpu irq handling at hotplug.

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Message-ID: <20160831144128.GE29505@arm.com>
Date:   Wed, 31 Aug 2016 15:41:28 +0100
From:   Will Deacon <will.deacon@....com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Yabin Cui <yabinc@...gle.com>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm/perf: Fix pmu percpu irq handling at hotplug.

On Tue, Aug 30, 2016 at 06:32:25PM +0100, Mark Rutland wrote:
> On Fri, Aug 26, 2016 at 10:48:00AM +0100, Will Deacon wrote:
> > On Fri, Aug 19, 2016 at 03:25:14PM +0100, Mark Rutland wrote:
> > > On Thu, Aug 18, 2016 at 01:24:38PM -0700, Yabin Cui wrote:
> > > >    If the cpu pmu is using a percpu irq:                                    
> > > >          
> > > >    1. When a cpu is down, we should disable pmu irq on                      
> > > >    that cpu. Otherwise, if the cpu is still down when                        
> > > >    the last perf event is released, the pmu irq can't                        
> > > >    be freed. Because the irq is still enabled on the                        
> > > >    offlined cpu. And following perf_event_open()                            
> > > >    syscalls will fail.                                                      
> > > >
> > > >    2. When a cpu is up, we should enable pmu irq on                          
> > > >    that cpu. Otherwise, profiling tools can't sample                        
> > > >    events on the cpu before all perf events are                              
> > > >    released, because pmu irq is disabled on that cpu.                        
> 
> [...]
> 
> > > Rather than adding more moving parts to the IRQ manipulation logic, I'd
> > > rather we rework the IRQ manipulation logic to:
> > > 
> > > * At probe time, request all the interrupts. If we can't, bail out and
> > >   fail the probe.
> > > 
> > > * Upon hotplug in (and at probe time), configure the affinity and
> > >   enable the relevant interrupt(s).
> > > 
> > > * Upon hotplug out, disable the relevant interrupt.
> 
> > > I'm taking a look at doing the above, but I don't yet have a patch.
> > 
> > Any update on this? I'd quite like to do *something* to fix the issues
> > reported here.
> 
> Apologies for the delay.
> 
> I've been away from my development hardware for the last week, so I
> ahven't fought with this for a few days.
> 
> Given it's requiring that I practically rewrite of_pmu_irq_cfg and
> friends, it may be better to take Yabin's patch for the timebeing if you
> want a quick fix for this particular issue.

Right, but that patch is totally mangled :/

I guess this will have to wait until somebody has time to rework the IRQ
code.

Will