linux-kernel - Re: [PATCH RFC DNM] perf: Add support for Qualcomm Last-Level Cache Controller PMU

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Message-ID: <379ac43f-2b21-420b-a487-bec37b8c94a7@linaro.org>
Date:   Fri, 25 Aug 2023 19:09:05 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Trilok Soni <quic_tsoni@...cinc.com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>
Cc:     Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH RFC DNM] perf: Add support for Qualcomm Last-Level Cache
 Controller PMU

On 25.08.2023 19:07, Trilok Soni wrote:
> On 8/25/2023 4:50 AM, Konrad Dybcio wrote:
>> On 24.08.2023 23:31, Trilok Soni wrote:
>>> On 8/9/2023 1:09 PM, Konrad Dybcio wrote:
>>>> Add support for the Qualcomm LLCC (Last-Level Cache Controller) PMU,
>>>> which provides a single event, expressing cache read misses.
>>>>
>>>> Based on the vendor driver found in the msm-5.10 downstream kernel.
>>>>
>>>> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
>>>> ---
>>>> Hi, I've been trying to get this driver going upstream by cleaning it
>>>> up and adding the necessary perf boilerplate (the original Qualcomm one
>>>> only pokes at the PMU from within the kernel itself) to use the
>>>> userspace tool.
>>>>
>>>> I can not however get it to cooperate.. in this iteration I get a PMU
>>>> event registered (though with only a "raw" name - no "x OR y" like with
>>>> other PMUs on the system) as:
>>>>
>>>> llcc_pmu/read_miss/                                [Kernel PMU event]
>>>>
>>>> but the .read callback is never called when I run:
>>>>
>>>> sudo perf stat -C 0 -a -e llcc_pmu/read_miss/ stress-ng -C 8 -c 8 -m 10
>>>>
>>>> which always returns 0
>>>>
>>>> if I add --always-kernel I get:
>>>> <not supported>      llcc_pmu/read_miss/
>>>
>>> Which SOC you are trying this on?
>> 8250
> 
> Thanks. Let me see if my team can try this on latest SOCs and if it is the same behavior. Did you tried reading the counter by "printk" in the kernel and see the values are dumped from the register?
Thanks for looking into this.

I debugbombed all the interesting functions and somehow the ones
which interface with the hardware are not even called as part of
executing `perf [...]` :/

Konrad