Re: [RFC PATCH] arm64: defconfig: Disable fine-grained task level IRQ time accounting

[Marc Zyngier]

On 2020-08-03 12:48, Valentin Schneider wrote:
> On 03/08/20 12:38, Vladimir Oltean wrote:
> > On Mon, Aug 03, 2020 at 10:51:32AM +0100, Robin Murphy wrote:
> > > Having glanced across another thread that mentions IRQ accounting
> > > recently[1], I wonder if the underlying bug here might have something 
> > > do to
> > > with the stuff that Marc's trying to clean up.
> > >
> > > Robin.
> > >
> > > [1] 
> > > https://lore.kernel.org/linux-arm-kernel/20200624195811.435857-16-maz@xxxxxxxxxx/
> >
> > Thanks Robin. I've applied Marc's "[PATCH v2 00/17] arm/arm64: Turning
> > IPIs into normal interrupts" series and the LS1028A I'm debugging 
> > hangs
> > in absolutely the same way.
>
> I'm not too surprised by that, wrt accounting this mostly changes where 
> the
> stores go to and barely shuffles when they happen (slightly earlier on 
> the
> IPI handling path).

Indeed. This series is just a "let's make things be the way they should 
be",
and isn't really fixing any bug. It actually may introduce a couple...

> FWIW I've had 'stress-ng --hrtimers 1' running on my Juno and eMAG for 
> ~15
> minutes and haven't had a splat yet.

I've started a couple of VMs with that workload too. 400K irq/s on an
8 vcpu guest, nothing to report so far.

But removing IRQ_TIME_ACCOUNTING from defconfig is a resounding "no 
way!".
It looks like we have a bug, and it should be squashed, not glanced 
over.

        M.
--
Jazz is not dead. It just smells funny...