linux-kernel - Re: [PATCH v2] blktrace: Don't output messages if NOTIFY isn't set.

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Date:	Tue, 18 Jan 2011 22:36:51 -0700
From:	Jens Axboe <axboe@...nel.dk>
To:	Tao Ma <tm@....ma>
CC:	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	Jeff Moyer <jmoyer@...hat.com>
Subject: Re: [PATCH v2] blktrace: Don't output messages if NOTIFY isn't set.

On 2011-01-18 20:09, Tao Ma wrote:
> Hi Jeff,
> On 01/18/2011 11:50 PM, Jeff Moyer wrote:
>> Tao Ma<tm@....ma>  writes:
>>
>>> +	/*
>>> +	 * 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.
> I was thinking of this, but actually there is no way for the user to set this flag.
> At least from blktrace(8), -a doesn't have any flags like NOTIFY. So if the user
> set any flag, NOTIFY will be cleared. So it does work. Thanks.
> 
> Here is the updated patch.
> 
> From 8693c19f165b09f60d5c26aed369d79a79e144ba Mon Sep 17 00:00:00 2001
> From: Tao Ma <boyu.mt@...bao.com>
> Date: Wed, 19 Jan 2011 10:51:44 +0800
> Subject: [PATCH v2] blktrace: Don't output messages if NOTIFY isn't set.
> 
> 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 BLK_TC_NOTIFY isn't set.
> 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: Jeff Moyer <jmoyer@...hat.com>
> Signed-off-by: Tao Ma <boyu.mt@...bao.com>
> ---
>  kernel/trace/blktrace.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index 153562d..d95721f 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -138,6 +138,13 @@ void __trace_note_message(struct blk_trace *bt, const char *fmt, ...)
>  		     !blk_tracer_enabled))
>  		return;
>  
> +	/*
> +	 * If the BLK_TC_NOTIFY action mask isn't set, don't send any note
> +	 * message to the trace.
> +	 */
> +	if (!(bt->act_mask & BLK_TC_NOTIFY))
> +		return;
> +
>  	local_irq_save(flags);
>  	buf = per_cpu_ptr(bt->msg_data, smp_processor_id());
>  	va_start(args, fmt);

Hmm, it should only mask messages, not task/timestamp notifies. This
will mask all of them.

The message mask I agree with, but the other ones should essentially be
unmaskable.

-- 
Jens Axboe

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