linux-kernel - Re: [PATCHv8 2/5] arm64: dts: qcom: msm8998: Add Coresight support

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Date:   Thu, 18 Jul 2019 15:23:49 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>,
        gregkh@...uxfoundation.org, mathieu.poirier@...aro.org,
        leo.yan@...aro.org, alexander.shishkin@...ux.intel.com,
        mike.leach@...aro.org, robh+dt@...nel.org,
        bjorn.andersson@...aro.org, devicetree@...r.kernel.org,
        david.brown@...aro.org, mark.rutland@....com
Cc:     rnayak@...eaurora.org, vivek.gautam@...eaurora.org,
        sibis@...eaurora.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        marc.w.gonzalez@...e.fr
Subject: Re: [PATCHv8 2/5] arm64: dts: qcom: msm8998: Add Coresight support

Hi,

On 7/18/2019 3:07 PM, Suzuki K Poulose wrote:
> 
> 
> Using the sysfs doesn't guarantee that the ETR actually uses SG mode, 
> unless
> the buffer size selected is > 1M, which is why I am more interested in the
> perf usage. Alternatively you may configure a larger buffer size (say, 
> 8MB) via:
> 
> echo 0x800000 > /sys/bus/coresight/.../tmc_etr0/buffer_size
> 

Yes, you had mentioned about setting buffer size > 1M in the same 
thread[1] and I had followed the same.

[1] https://lkml.org/lkml/2019/1/18/311

> 
>>
>> As said in one of the series initially [1], QCOM msm downstream kernels
>> have been using scatter gather mode and we haven't seen any fatal issues.
>>
>> [1] https://patchwork.kernel.org/patch/10769535/
> 
> I haven't seen any test results there either.
> 

You did not ask for it there ;)

I do not have the test results handy now and those platforms.
I will arrange for them and post some test results.

Just to confirm, do you need some traces or just the buffer size
and sink set?

Thanks,
Sai

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