linux-kernel - Re: [PATCH V5 - RESEND 2/3] coresight: etm: Make cycle count threshold user configurable

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Date:   Wed, 20 Sep 2023 16:14:56 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mike Leach <mike.leach@...aro.org>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        coresight@...ts.linaro.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V5 - RESEND 2/3] coresight: etm: Make cycle count
 threshold user configurable



On 9/20/23 14:52, Suzuki K Poulose wrote:
> On 15/09/2023 10:36, Anshuman Khandual wrote:
>> Cycle counting is enabled, when requested and supported but with a default
>> threshold value ETM_CYC_THRESHOLD_DEFAULT i.e 0x100 getting into TRCCCCTLR,
>> representing the minimum interval between cycle count trace packets.
> 
> minor nit:
> 
> When Cycle counting is enabled, we use a default threshold value (0x100) for the instruction trace cycle counting.
>>
>> This makes cycle threshold user configurable, from the user space via perf
>> event attributes. Although it falls back using ETM_CYC_THRESHOLD_DEFAULT,
>> in case no explicit request.
> 
> Minor nit:
> 
> This patch makes the cycle threshold user configurable via perf event
> attributes( 'cc_threshold' => event->attr.config3[11:0] ), falling back
> to the the current default if unspecified.
> 
> 
> 
>> As expected it creates a sysfs file as well.
> 
> 
>>
>> /sys/bus/event_source/devices/cs_etm/format/cc_threshold
>>
>> New 'cc_threshold' uses 'event->attr.config3' as no more space is available
>> in 'event->attr.config1' or 'event->attr.config2'.
> 
> Trim the above part.
> 
> 
> Rest looks fine to me.

Will change the commit message as follows.


    coresight: etm: Make cycle count threshold user configurable
    
    When cycle counting is enabled, we use a default threshold value i.e 0x100
    for the instruction trace cycle counting.
    
    This patch makes the cycle threshold user configurable via perf event
    attributes( 'cc_threshold' => event->attr.config3[11:0] ), falling back
    to the current default if unspecified.