Re: Why blktrace didn't trace requests merge?
From: Jens Axboe
Date: Mon Sep 17 2012 - 14:28:13 EST
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
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