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

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Message-ID: <VI1PR09MB263873B89C6CF4D557F811C5C74D9@VI1PR09MB2638.eurprd09.prod.outlook.com>
Date:   Thu, 15 Apr 2021 17:20:31 +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!

On 15/04/2021 10:28, Suthikulpanit, Suravee wrote:
> David,
> 
> On 4/14/2021 10:33 PM, David Coe wrote:
>> 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,
>>
> 
> For the Ryzen 2400G, could you please try with:
> - 1 event at a time
> - Not more than 8 events (On your system, it has 2 banks x 4 counters/bank.
> I am trying to see if this issue might be related to the counters 
> multiplexing).
> 
> Thanks,

Herewith similar one-at-a-time perf stat results for the Ryzen 4700U. As 
before, more than 8 events displays the third (%) column and (sometimes) 
'silly' numbers in the first column.

-- 
David

View attachment "EventList-4700U.txt" of type "text/plain" (5650 bytes)