linux-kernel - Re: [PATCH 2/2] iommu/amd: Remove performance counter pre-initialization test

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Date:   Wed, 14 Apr 2021 16:33:26 +0100
From:   David Coe <david.coe@...e.co.uk>
To:     "Suthikulpanit, Suravee" <suravee.suthikulpanit@....com>,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org
Cc:     joro@...tes.org, will@...nel.org, jsnitsel@...hat.com,
        pmenzel@...gen.mpg.de, Jon.Grimm@....com,
        Tj <ml.linux@...oe.vision>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Alexander Monakov <amonakov@...ras.ru>,
        Alex Hung <1917203@...s.launchpad.net>
Subject: Re: [PATCH 2/2] iommu/amd: Remove performance counter
 pre-initialization test

Hi Suravee!

I've re-run your revert+update patch on Ubuntu's latest kernel 5.11.0-14 
partly to check my mailer's 'mangling' hadn't also reached the code!

There are 3 sets of results in the attachment, all for the Ryzen 2400G. 
The as-distributed kernel already incorporates your IOMMU RFCv3 patch.

A. As-distributed kernel (cold boot)
    >5 retries, so no IOMMU read/write capability, no amd_iommu events.

B. As-distributed kernel (warm boot)
    <5 retries, amd_iommu running stats show large numbers as before.

C. Revert+Update kernel
    amd_iommu events listed and also show large hit/miss numbers.

In due course, I'll load the new (revert+update) kernel on the 4700G but 
won't overload your mail-box unless something unusual turns up.

Best regards,

-- 
David

View attachment "2400G-5.11.0-14.txt" of type "text/plain" (10025 bytes)