linux-kernel - Re: [PATCH] blktrace: Send BLK_TN_PROCESS events to all running traces

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Date:	Mon, 23 Sep 2013 09:02:08 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Jens Axboe <axboe@...nel.dk>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] blktrace: Send BLK_TN_PROCESS events to all running traces

Jan Kara <jack@...e.cz> writes:

> Currently each task sends BLK_TN_PROCESS event to the first traced
> device it interacts with after a new trace is started. When there are
> several traced devices and the task accesses more devices, this logic
> can result in BLK_TN_PROCESS being sent several times to some devices
> while it is never sent to other devices. Thus blkparse doesn't display
> command name when parsing some blktrace files.
>
> Fix the problem by sending BLK_TN_PROCESS event to all traced devices
> when a task interacts with any of them.
>
> Signed-off-by: Jan Kara <jack@...e.cz>

[snip]

> @@ -229,16 +241,15 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
>  		goto record_it;
>  	}
>  
> +	if (unlikely(tsk->btrace_seq != blktrace_seq))
> +		trace_note_tsk(tsk);
> +
>  	/*
>  	 * A word about the locking here - we disable interrupts to reserve
>  	 * some space in the relay per-cpu buffer, to prevent an irq
>  	 * from coming in and stepping on our toes.
>  	 */
>  	local_irq_save(flags);
> -
> -	if (unlikely(tsk->btrace_seq != blktrace_seq))
> -		trace_note_tsk(bt, tsk);
> -
>  	t = relay_reserve(bt->rchan, sizeof(*t) + pdu_len);
>  	if (t) {
>  		sequence = per_cpu_ptr(bt->sequence, cpu);

I don't think moving the call site was strictly necessary.  That
wouldn't really change anything, though.  I also think that this
simplistic approach is good enough.

Reviewed-by: Jeff Moyer <jmoyer@...hat.com>
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