linux-kernel - Re: [PATCH] iommu/amd: Fix event counter availability check

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Date:   Tue, 2 Jun 2020 17:51:59 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Alexander Monakov <amonakov@...ras.ru>,
        linux-kernel@...r.kernel.org
Cc:     Joerg Roedel <joro@...tes.org>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        iommu@...ts.linux-foundation.org, skhan@...uxfoundation.org
Subject: Re: [PATCH] iommu/amd: Fix event counter availability check

On 5/31/20 1:22 AM, Alexander Monakov wrote:
> Hi,
> 
> Adding Shuah Khan to Cc: I've noticed you've seen this issue on Ryzen 2400GE;
> can you have a look at the patch? Would be nice to know if it fixes the
> problem for you too.
> 

I am not seeing any change in behavior on my system. I still see:

I can't read perf counters.

The question I asked in my previous thread on this:

--------------------------------------------------------------------
I see 2 banks and 4 counters on my system. Is it sufficient to check
the first bank and first counter? In other words, if the first one
isn't writable, are all counters non-writable?

Should we read the config first and then, try to see if any of the
counters are writable? I have a patch that does that, I can send it
out for review.

I changed the logic to read config to get max banks and counters
before checking if counters are writable and tried writing to all.
The result is the same and all of them aren't writable. However,
when disable the writable check and assume they are, I can run

perf stat -e 'amd_iommu_0 on all events and get data.

perf stat -e 'amd_iommu_0/cmd_processed/' sleep 10

  Performance counter stats for 'system wide':

                 56      amd_iommu_0/cmd_processed/

       10.001525171 seconds time elapsed

perf stat -a -e amd_iommu/mem_trans_total/ sleep 10

  Performance counter stats for 'system wide':

              2,696      amd_iommu/mem_trans_total/

       10.001465115 seconds time elapsed

I tried all possible events listed under amd_iommu_0 and I can get
data on all of them. No problems in dmesg.
--------------------------------------------------------------------

This patch doesn't really address that question.

thanks,
-- Shuah