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Date:   Wed, 10 Feb 2021 18:09:23 +0000
From:   Avri Altman <Avri.Altman@....com>
To:     Adrian Hunter <adrian.hunter@...el.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        "James E . J . Bottomley" <jejb@...ux.ibm.com>
CC:     "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Bean Huo <huobean@...il.com>, Can Guo <cang@...eaurora.org>,
        Stanley Chu <stanley.chu@...iatek.com>
Subject: RE: [PATCH V2 1/4] scsi: ufs: Add exception event tracepoint

> 
> Currently, exception event status can be read from wExceptionEventStatus
> attribute (sysfs file attributes/exception_event_status under the UFS host
> controller device directory). Polling that attribute to track UFS exception
> events is impractical, so add a tracepoint to track exception events for
> testing and debugging purposes.
> 
> Note, by the time the exception event status is read, the exception event
> may have cleared, so the value can be zero - see example below.
> 
> Note also, only enabled exception events can be reported. A subsequent
> patch adds the ability for users to enable selected exception events via
> debugfs.
> 
> Example with driver instrumented to enable all exception events:
> 
>   # echo 1 >
> /sys/kernel/debug/tracing/events/ufs/ufshcd_exception_event/enable
> 
>   ... do some I/O ...
> 
>   # cat /sys/kernel/debug/tracing/trace
>   # tracer: nop
>   #
>   # entries-in-buffer/entries-written: 3/3   #P:5
>   #
>   #                                _-----=> irqs-off
>   #                               / _----=> need-resched
>   #                              | / _---=> hardirq/softirq
>   #                              || / _--=> preempt-depth
>   #                              ||| /     delay
>   #           TASK-PID     CPU#  ||||   TIMESTAMP  FUNCTION
>   #              | |         |   ||||      |         |
>        kworker/2:2-173     [002] ....   731.486419: ufshcd_exception_event:
> 0000:00:12.5: status 0x0
>        kworker/2:2-173     [002] ....   732.608918: ufshcd_exception_event:
> 0000:00:12.5: status 0x4
>        kworker/2:2-173     [002] ....   732.609312: ufshcd_exception_event:
> 0000:00:12.5: status 0x4
> 
> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
Reviewed-by: Avri Altman <avri.altman@....com>

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