Why blktrace didn't trace requests merge?

Why blktrace didn't trace requests merge?

[Jianpeng Ma]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="gb2312", Size: 308 bytes --]

Hi all:
	I used blktrace to trace some io.But i can't find requests merge. I searched the code and did't not find.
	Why? 
									
Thanks!
Jianpengÿôèº{.nÇ+‰·Ÿ®‰­†+%ŠËÿ±éݶ\x17¥Šwÿº{.nÇ+‰·¥Š{±þG«éÿŠ{ayº\x1dʇڙë,j\a­¢f£¢·hšïêÿ‘êçz_è®\x03(­éšŽŠÝ¢j"ú\x1a¶^[m§ÿÿ¾\a«þG«éÿ¢¸?™¨è­Ú&£ø§~á¶iO•æ¬z·švØ^\x14\x04\x1a¶^[m§ÿÿÃ\fÿ¶ìÿ¢¸?–I¥

Re: Why blktrace didn't trace requests merge?

[Steven Rostedt]

On Mon, 2012-09-17 at 19:33 +0800, Jianpeng Ma wrote:
> Hi all:
> 	I used blktrace to trace some io.But i can't find requests merge. I searched the code and did't not find.
> 	Why? 
> 									

No idea. I don't use blktrace much, but I Cc'd those that understand it
better than I.

-- Steve

Re: Why blktrace didn't trace requests merge?

[Tejun Heo]

(cc'ing Jens)

On Mon, Sep 17, 2012 at 09:22:28AM -0400, Steven Rostedt wrote:
> On Mon, 2012-09-17 at 19:33 +0800, Jianpeng Ma wrote:
> > Hi all:
> > 	I used blktrace to trace some io.But i can't find requests merge. I searched the code and did't not find.
> > 	Why? 
> > 									
> 
> No idea. I don't use blktrace much, but I Cc'd those that understand it
> better than I.

-- 
tejun

Re: Why blktrace didn't trace requests merge?

[KOSAKI Motohiro]

(9/17/12 1:55 PM), Tejun Heo wrote:
> (cc'ing Jens)
> 
> On Mon, Sep 17, 2012 at 09:22:28AM -0400, Steven Rostedt wrote:
>> On Mon, 2012-09-17 at 19:33 +0800, Jianpeng Ma wrote:
>>> Hi all:
>>> 	I used blktrace to trace some io.But i can't find requests merge. I searched the code and did't not find.
>>> 	Why? 
>>> 									
>>
>> No idea. I don't use blktrace much, but I Cc'd those that understand it
>> better than I.

backmerge/fronmerge event?

Re: Why blktrace didn't trace requests merge?

[Jens Axboe]

On 2012-09-17 19:55, Tejun Heo wrote:
> (cc'ing Jens)
> 
> On Mon, Sep 17, 2012 at 09:22:28AM -0400, Steven Rostedt wrote:
>> On Mon, 2012-09-17 at 19:33 +0800, Jianpeng Ma wrote:
>>> Hi all:
>>> 	I used blktrace to trace some io.But i can't find requests merge. I searched the code and did't not find.
>>> 	Why? 
>>> 									
>>
>> No idea. I don't use blktrace much, but I Cc'd those that understand it
>> better than I.

Works for me:

[...]


  8,0    0       26     0.009147735   664  A  WS 315226143 + 8 <- (8,7) 19406344
  8,0    0       27     0.009148677   664  Q  WS 315226143 + 8 [btrfs-submit-1]
  8,0    0       28     0.009152967   664  G  WS 315226143 + 8 [btrfs-submit-1]
  8,0    0       29     0.009154242   664  P   N [btrfs-submit-1]
  8,0    0       30     0.009155538   664  A  WS 315226151 + 8 <- (8,7) 19406352
  8,0    0       31     0.009155743   664  Q  WS 315226151 + 8 [btrfs-submit-1]
  8,0    0       32     0.009157086   664  M  WS 315226151 + 8 [btrfs-submit-1]
  8,0    0       33     0.009158716   664  I  WS 315226143 + 16 [btrfs-submit-1]

That's from a quick trace of /dev/sda. I started blktrace, then did:

$ dd if=/dev/zero of=foo bs=4k count=128 && sync

to ensure that I knew merges would be happening. Output stats at the end:

Total (sda):
 Reads Queued:           7,       44KiB  Writes Queued:         447,     7692KiB
 Read Dispatches:        7,       44KiB  Write Dispatches:      416,     7692KiB
 Reads Requeued:         0               Writes Requeued:         0
 Reads Completed:        7,       44KiB  Writes Completed:      435,     5864KiB
 Read Merges:            0,        0KiB  Write Merges:           23,      428KiB
 IO unplugs:            78               Timer unplugs:           0

-- 
Jens Axboe

Re: Re: Why blktrace didn't trace requests merge?

[Jianpeng Ma]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="gb2312", Size: 2177 bytes --]

On 2012-09-18 02:27 Jens Axboe <axboe@kernel.dk> Wrote:
>On 2012-09-17 19:55, Tejun Heo wrote:
>> (cc'ing Jens)
>> 
>> On Mon, Sep 17, 2012 at 09:22:28AM -0400, Steven Rostedt wrote:
>>> On Mon, 2012-09-17 at 19:33 +0800, Jianpeng Ma wrote:
>>>> Hi all:
>>>> 	I used blktrace to trace some io.But i can't find requests merge. I searched the code and did't not find.
>>>> 	Why? 
>>>> 									
>>>
>>> No idea. I don't use blktrace much, but I Cc'd those that understand it
>>> better than I.
>
>Works for me:
>
>[...]
>
>
>  8,0    0       26     0.009147735   664  A  WS 315226143 + 8 <- (8,7) 19406344
>  8,0    0       27     0.009148677   664  Q  WS 315226143 + 8 [btrfs-submit-1]
>  8,0    0       28     0.009152967   664  G  WS 315226143 + 8 [btrfs-submit-1]
>  8,0    0       29     0.009154242   664  P   N [btrfs-submit-1]
>  8,0    0       30     0.009155538   664  A  WS 315226151 + 8 <- (8,7) 19406352
>  8,0    0       31     0.009155743   664  Q  WS 315226151 + 8 [btrfs-submit-1]
>  8,0    0       32     0.009157086   664  M  WS 315226151 + 8 [btrfs-submit-1]
>  8,0    0       33     0.009158716   664  I  WS 315226143 + 16 [btrfs-submit-1]
>
>That's from a quick trace of /dev/sda. I started blktrace, then did:
>
>$ dd if=/dev/zero of=foo bs=4k count=128 && sync
>
>to ensure that I knew merges would be happening. Output stats at the end:
>
>Total (sda):
> Reads Queued:           7,       44KiB  Writes Queued:         447,     7692KiB
> Read Dispatches:        7,       44KiB  Write Dispatches:      416,     7692KiB
> Reads Requeued:         0               Writes Requeued:         0
> Reads Completed:        7,       44KiB  Writes Completed:      435,     5864KiB
> Read Merges:            0,        0KiB  Write Merges:           23,      428KiB
> IO unplugs:            78               Timer unplugs:           0
>
>-- 
>Jens Axboe
>
First, Thanks your time!
If i understand correctly, the merge of your example is bio with request, not request wiht request.
Yes or no?

Thanks!
Jianpeng
ÿôèº{.nÇ+‰·Ÿ®‰­†+%ŠËÿ±éݶ\x17¥Šwÿº{.nÇ+‰·¥Š{±þG«éÿŠ{ayº\x1dʇڙë,j\a­¢f£¢·hšïêÿ‘êçz_è®\x03(­éšŽŠÝ¢j"ú\x1a¶^[m§ÿÿ¾\a«þG«éÿ¢¸?™¨è­Ú&£ø§~á¶iO•æ¬z·švØ^\x14\x04\x1a¶^[m§ÿÿÃ\fÿ¶ìÿ¢¸?–I¥

Re: Why blktrace didn't trace requests merge?

[Jens Axboe]

On 2012-09-18 02:30, Jianpeng Ma wrote:
> On 2012-09-18 02:27 Jens Axboe <axboe@kernel.dk> Wrote:
>> On 2012-09-17 19:55, Tejun Heo wrote:
>>> (cc'ing Jens)
>>>
>>> On Mon, Sep 17, 2012 at 09:22:28AM -0400, Steven Rostedt wrote:
>>>> On Mon, 2012-09-17 at 19:33 +0800, Jianpeng Ma wrote:
>>>>> Hi all:
>>>>> 	I used blktrace to trace some io.But i can't find requests merge. I searched the code and did't not find.
>>>>> 	Why? 
>>>>> 									
>>>>
>>>> No idea. I don't use blktrace much, but I Cc'd those that understand it
>>>> better than I.
>>
>> Works for me:
>>
>> [...]
>>
>>
>>  8,0    0       26     0.009147735   664  A  WS 315226143 + 8 <- (8,7) 19406344
>>  8,0    0       27     0.009148677   664  Q  WS 315226143 + 8 [btrfs-submit-1]
>>  8,0    0       28     0.009152967   664  G  WS 315226143 + 8 [btrfs-submit-1]
>>  8,0    0       29     0.009154242   664  P   N [btrfs-submit-1]
>>  8,0    0       30     0.009155538   664  A  WS 315226151 + 8 <- (8,7) 19406352
>>  8,0    0       31     0.009155743   664  Q  WS 315226151 + 8 [btrfs-submit-1]
>>  8,0    0       32     0.009157086   664  M  WS 315226151 + 8 [btrfs-submit-1]
>>  8,0    0       33     0.009158716   664  I  WS 315226143 + 16 [btrfs-submit-1]
>>
>> That's from a quick trace of /dev/sda. I started blktrace, then did:
>>
>> $ dd if=/dev/zero of=foo bs=4k count=128 && sync
>>
>> to ensure that I knew merges would be happening. Output stats at the end:
>>
>> Total (sda):
>> Reads Queued:           7,       44KiB  Writes Queued:         447,     7692KiB
>> Read Dispatches:        7,       44KiB  Write Dispatches:      416,     7692KiB
>> Reads Requeued:         0               Writes Requeued:         0
>> Reads Completed:        7,       44KiB  Writes Completed:      435,     5864KiB
>> Read Merges:            0,        0KiB  Write Merges:           23,      428KiB
>> IO unplugs:            78               Timer unplugs:           0
>>
>> -- 
>> Jens Axboe
>>
> First, Thanks your time!
> If i understand correctly, the merge of your example is bio with
> request, not request wiht request.  Yes or no?

It is bio to request, correct. Request to request merges are relatively
more rare.

-- 
Jens Axboe

Re: Re: Why blktrace didn't trace requests merge?

[Jianpeng Ma]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="gb2312", Size: 2508 bytes --]

On 2012-09-18 13:49 Jens Axboe <axboe@kernel.dk> Wrote:
>On 2012-09-18 02:30, Jianpeng Ma wrote:
>> On 2012-09-18 02:27 Jens Axboe <axboe@kernel.dk> Wrote:
>>> On 2012-09-17 19:55, Tejun Heo wrote:
>>>> (cc'ing Jens)
>>>>
>>>> On Mon, Sep 17, 2012 at 09:22:28AM -0400, Steven Rostedt wrote:
>>>>> On Mon, 2012-09-17 at 19:33 +0800, Jianpeng Ma wrote:
>>>>>> Hi all:
>>>>>> 	I used blktrace to trace some io.But i can't find requests merge. I searched the code and did't not find.
>>>>>> 	Why? 
>>>>>> 									
>>>>>
>>>>> No idea. I don't use blktrace much, but I Cc'd those that understand it
>>>>> better than I.
>>>
>>> Works for me:
>>>
>>> [...]
>>>
>>>
>>>  8,0    0       26     0.009147735   664  A  WS 315226143 + 8 <- (8,7) 19406344
>>>  8,0    0       27     0.009148677   664  Q  WS 315226143 + 8 [btrfs-submit-1]
>>>  8,0    0       28     0.009152967   664  G  WS 315226143 + 8 [btrfs-submit-1]
>>>  8,0    0       29     0.009154242   664  P   N [btrfs-submit-1]
>>>  8,0    0       30     0.009155538   664  A  WS 315226151 + 8 <- (8,7) 19406352
>>>  8,0    0       31     0.009155743   664  Q  WS 315226151 + 8 [btrfs-submit-1]
>>>  8,0    0       32     0.009157086   664  M  WS 315226151 + 8 [btrfs-submit-1]
>>>  8,0    0       33     0.009158716   664  I  WS 315226143 + 16 [btrfs-submit-1]
>>>
>>> That's from a quick trace of /dev/sda. I started blktrace, then did:
>>>
>>> $ dd if=/dev/zero of=foo bs=4k count=128 && sync
>>>
>>> to ensure that I knew merges would be happening. Output stats at the end:
>>>
>>> Total (sda):
>>> Reads Queued:           7,       44KiB  Writes Queued:         447,     7692KiB
>>> Read Dispatches:        7,       44KiB  Write Dispatches:      416,     7692KiB
>>> Reads Requeued:         0               Writes Requeued:         0
>>> Reads Completed:        7,       44KiB  Writes Completed:      435,     5864KiB
>>> Read Merges:            0,        0KiB  Write Merges:           23,      428KiB
>>> IO unplugs:            78               Timer unplugs:           0
>>>
>>> -- 
>>> Jens Axboe
>>>
>> First, Thanks your time!
>> If i understand correctly, the merge of your example is bio with
>> request, not request wiht request.  Yes or no?
>
>It is bio to request, correct. Request to request merges are relatively
>more rare.
>
>-- 
>Jens Axboe
>
Thanks very much, I know.

Jianpengÿôèº{.nÇ+‰·Ÿ®‰­†+%ŠËÿ±éݶ\x17¥Šwÿº{.nÇ+‰·¥Š{±þG«éÿŠ{ayº\x1dʇڙë,j\a­¢f£¢·hšïêÿ‘êçz_è®\x03(­éšŽŠÝ¢j"ú\x1a¶^[m§ÿÿ¾\a«þG«éÿ¢¸?™¨è­Ú&£ø§~á¶iO•æ¬z·švØ^\x14\x04\x1a¶^[m§ÿÿÃ\fÿ¶ìÿ¢¸?–I¥