linux-kernel - Re: [PATCH 1/2] include: trace: Add SCMI header with trace events

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Date:   Mon, 23 Dec 2019 15:39:09 +0000
From:   Lukasz Luba <lukasz.luba@....com>
To:     Jim Quinlan <james.quinlan@...adcom.com>,
        Sudeep Holla <sudeep.holla@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        mingo@...hat.com, rostedt@...dmis.org
Subject: Re: [PATCH 1/2] include: trace: Add SCMI header with trace events


On 12/20/19 4:24 PM, Jim Quinlan wrote:
> 
>> Thank you for sharing your experiments and thoughts. I have probably
>> similar setup for stressing the communication channel, but I do also
>> some wired things in the firmware. That's why I need to measure these
>> delays. I am happy that it is useful for you also.
>>
>> I don't know if your firmware supports 'fast channel', but please keep
>> in mind that it is not tracked in this 'transfer_id'.
>> This transfer_id in v2 version does not show the real transfers
>> to the firmware since there is another path called 'fast channel' or
>> 'fast_switch' in the CPUfreq. It is in drivers/firmware/arm_scmi/perf.c
>> and the atomic variable is not incremented in that path. Adding it also
>> there just for atomic_inc() probably would add delays in the fast_switch
>> and also brings little value.
>> For the normal channel, where we have spinlocks and other stuff, this
>> atomic_inc() could stay in my opinion.
>>
>> Regards,
>> Lukasz
> Hi Lukasz,
> 
> We currently do not use "fast channels" - although it is possible we might someday.
> I find the transfer_id useful per your v2 even if it doesn't cover FC.  Thanks for
> submitting and discussing this!

Thank you for cooperation.

Regards,
Lukasz

> 
> Regards,
> Jim Quinlan
>