linux-kernel - Re: [PATCH] x86/events/amd/iommu: Fix invalid Perf result due to IOMMU PMC power-gating

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Date:   Tue, 4 May 2021 11:39:37 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Cc:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        iommu@...ts.linux-foundation.org, mingo@...hat.com,
        joro@...tes.org, Jon.Grimm@....com, amonakov@...ras.ru,
        David Coe <david.coe@...e.co.uk>
Subject: Re: [PATCH] x86/events/amd/iommu: Fix invalid Perf result due to
 IOMMU PMC power-gating

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?