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

[Jeff Moyer <jmoyer@redhat.com>]

Jens Axboe <axboe@kernel.dk> writes:

> On 2011-01-18 23:09, Tao Ma wrote:
>> 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@tao.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@taobao.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@kernel.dk>
>>>> Cc: Steven Rostedt<rostedt@goodmis.org>
>>>> Cc: Jeff Moyer<jmoyer@redhat.com>
>>>> Signed-off-by: Tao Ma<boyu.mt@taobao.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?
>
> You did, I missed that. Patch looks fine then, I'll queue it up. Thanks!

I was guessing at the use of BLK_TC_NOTIFY for this.  Should there be
another flag for these messages, so they aren't conflated with
task/timestamp notifications?

Cheers,
Jeff