From: Peter Zijlstra <peterz@infradead.org>
To: "Suthikulpanit, Suravee" <suravee.suthikulpanit@amd.com>
Cc: linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org,
iommu@lists.linux-foundation.org, mingo@redhat.com,
joro@8bytes.org, Jon.Grimm@amd.com, amonakov@ispras.ru,
David Coe <david.coe@live.co.uk>
Subject: Re: [PATCH] x86/events/amd/iommu: Fix invalid Perf result due to IOMMU PMC power-gating
Date: Tue, 4 May 2021 14:13:44 +0200 [thread overview]
Message-ID: <YJE6eCyHtIONCJet@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <e9769da5-3d2a-6e86-8ebd-feb00b567bba@amd.com>
On Tue, May 04, 2021 at 06:58:29PM +0700, Suthikulpanit, Suravee wrote:
> Peter,
>
> On 5/4/2021 4:39 PM, Peter Zijlstra wrote:
> > On Tue, May 04, 2021 at 01:52:36AM -0500, Suravee Suthikulpanit wrote:
> >
> > > 2. Since AMD IOMMU PMU does not support interrupt mode, the logic
> > > can be simplified to always start counting with value zero,
> > > and accumulate the counter value when stopping without the need
> > > to keep track and reprogram the counter with the previously read
> > > counter value.
> >
> > This relies on the hardware counter being the full 64bit wide, is it?
> >
>
> The HW counter value is 48-bit. Not sure why it needs to be 64-bit?
> I might be missing some points here? Could you please describe?
How do you deal with the 48bit overflow if you don't use the interrupt?
next prev parent reply other threads:[~2021-05-04 12:13 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-04 6:52 [PATCH] x86/events/amd/iommu: Fix invalid Perf result due to IOMMU PMC power-gating Suravee Suthikulpanit
2021-05-04 9:39 ` Peter Zijlstra
2021-05-04 11:58 ` Suthikulpanit, Suravee
2021-05-04 12:13 ` Peter Zijlstra [this message]
2021-05-05 12:39 ` Suthikulpanit, Suravee
2021-05-05 13:05 ` Peter Zijlstra
2021-05-10 2:08 ` Suthikulpanit, Suravee
2021-05-04 17:04 ` David Coe
2021-05-05 10:24 ` David Coe
2021-05-06 13:48 ` [tip: perf/urgent] " tip-bot2 for Suravee Suthikulpanit
2021-05-14 10:48 ` [PATCH] " David Coe
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