linux-kernel - Re: [PATCH] blktrace: Don't output messages if the user sets some action mask.

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Date:	Tue, 18 Jan 2011 10:50:01 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Tao Ma <tm@....ma>
Cc:	linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH] blktrace: Don't output messages if the user sets some action mask.

Tao Ma <tm@....ma> writes:

> From: Tao Ma <boyu.mt@...bao.com>
>
> Now if we enable blktrace, cfq has too many messages output to the
> trace buffer. It is fine if we don't specify any action mask.
> But if I do like this:
> blktrace /dev/sdb -a issue -a complete -o - | blkparse -i -
> I only want to see 'D' and 'C', while with the following command
> dd if=/mnt/ocfs2/test of=/dev/null bs=4k count=1 iflag=direct
>
> I will get(with a 2.6.37 vanilla kernel):
>   8,16   0        0     0.000000000     0  m   N cfq3805 alloced
>   8,16   0        0     0.000004126     0  m   N cfq3805 insert_request
>   8,16   0        0     0.000004884     0  m   N cfq3805 add_to_rr
>   8,16   0        0     0.000008417     0  m   N cfq workload slice:300
>   8,16   0        0     0.000009557     0  m   N cfq3805 set_active wl_prio:0 wl_type:2
>   8,16   0        0     0.000010640     0  m   N cfq3805 fifo=          (null)
>   8,16   0        0     0.000011193     0  m   N cfq3805 dispatch_insert
>   8,16   0        0     0.000012221     0  m   N cfq3805 dispatched a request
>   8,16   0        0     0.000012802     0  m   N cfq3805 activate rq, drv=1
>   8,16   0        1     0.000013181  3805  D   R 114759 + 8 [dd]
>   8,16   0        2     0.000164244     0  C   R 114759 + 8 [0]
>   8,16   0        0     0.000167997     0  m   N cfq3805 complete rqnoidle 0
>   8,16   0        0     0.000168782     0  m   N cfq3805 set_slice=100
>   8,16   0        0     0.000169874     0  m   N cfq3805 arm_idle: 8 group_idle: 0
>   8,16   0        0     0.000170189     0  m   N cfq schedule dispatch
>   8,16   0        0     0.000397938     0  m   N cfq3805 slice expired t=0
>   8,16   0        0     0.000399763     0  m   N cfq3805 sl_used=1 disp=1 charge=1 iops=0 sect=8
>   8,16   0        0     0.000400227     0  m   N cfq3805 del_from_rr
>   8,16   0        0     0.000400882     0  m   N cfq3805 put_queue
>
> See, there are 19 lines while I only need 2. I don't think it is
> appropriate for a user.
>
> So this patch will disable any messages if the user specify what he want to
> see. Now the output for the same command will look like:
>   8,16   0        1     0.000000000  4908  D   R 114759 + 8 [dd]
>   8,16   0        2     0.000146827     0  C   R 114759 + 8 [0]
>
> Yes, it is what I want to see.
>
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Signed-off-by: Tao Ma <boyu.mt@...bao.com>
> ---
>  kernel/trace/blktrace.c |    8 ++++++++
>  1 files changed, 8 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index 153562d..8219ffa 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -138,6 +138,14 @@ void __trace_note_message(struct blk_trace *bt, const char *fmt, ...)
>  		     !blk_tracer_enabled))
>  		return;
>  
> +	/*
> +	 * If the user does specify some action masks, don't send any note
> +	 * message to the trace so that it won't pollute what the user really
> +	 * want to see.
> +	 */
> +	if (bt->act_mask != (u16) -1)
> +		return;
> +

I think you want to check for the BLK_TC_NOTIFY bit.

Cheers,
Jeff
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