From: Marc Zyngier <maz@kernel.org>
To: Aman Priyadarshi <apeureka@amazon.de>
Cc: Alexander Graf <graf@amazon.com>,
kvmarm@lists.cs.columbia.edu, Ali Saidi <alisaidi@amazon.com>
Subject: Re: KVM: arm64: pmu: Reset sample period on overflow handling
Date: Wed, 16 Jun 2021 12:03:08 +0100 [thread overview]
Message-ID: <87k0mum5qr.wl-maz@kernel.org> (raw)
In-Reply-To: <094d40a0e7f5389ce5a13d96b96d4b7588c71d74.camel@amazon.de>
On Wed, 16 Jun 2021 11:52:42 +0100,
Aman Priyadarshi <apeureka@amazon.de> wrote:
>
> On Wed, 2021-06-16 at 11:31 +0100, Marc Zyngier wrote:
> >
> > Hi Aman,
> >
> > On Wed, 16 Jun 2021 10:17:28 +0100,
> > Aman Priyadarshi <apeureka@amazon.de> wrote:
> > >
> > > Hi Marc,
> > >
> > > On Tue, 2021-06-15 at 18:05 +0100, Marc Zyngier wrote:
> > > >
> > > > Can you reproduce the issue with vanilla guest kernels? It'd be
> > > > interesting to understand what makes it work on the guest side. Can
> > > > you please bisect it?
> > > >
> > >
> > > yes, I was able to narrow it down to the commit 0cbb058be904 ("arm64:
> > > perf:
> > > Disable PMU while processing counter overflows"), which fixes the
> > > problem
> > > on the guest side.
> >
> > Which is 3cce50dfec4a5b0414c974190940f47dd32c6dee in mainline. This
> > doesn't seem to have ever been backported before 4.18. So I don't know
> > why your 4.15 kernel was correctly behaving, but it could be that the
> > distro had randomly picked up the correct patch!
>
> Yes. https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1836117
Right. I guess that's their "value add".
> > You may want to backport it to 4.14.y and let Greg know about that.
> >
>
> Ack.
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
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prev parent reply other threads:[~2021-06-16 11:03 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-15 15:15 KVM: arm64: pmu: Reset sample period on overflow handling Aman Priyadarshi
2021-06-15 17:05 ` Marc Zyngier
2021-06-16 9:17 ` Aman Priyadarshi
2021-06-16 10:31 ` Marc Zyngier
2021-06-16 10:52 ` Aman Priyadarshi
2021-06-16 11:03 ` Marc Zyngier [this message]
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