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

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Date:	Wed, 19 Jan 2011 14:09:03 +0800
From:	Tao Ma <tm@....ma>
To:	Jens Axboe <axboe@...nel.dk>
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 01/19/2011 01:36 PM, Jens Axboe wrote:
> 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.
uh, yes, that's the reason why I put the check in __trace_note_message, 
not in trace_note. trace_note_time and trace_note_tsk will handle 
time/task issue and then call trace_note with the appropriate action 
mask. Do I miss something here?
>
> The message mask I agree with, but the other ones should essentially be
> unmaskable.
yeah, agree.

Regards,
Tao
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