On 2012-09-18 13:49 Jens Axboe <ax...@kernel.dk> Wrote: >On 2012-09-18 02:30, Jianpeng Ma wrote: >> On 2012-09-18 02:27 Jens Axboe <ax...@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.
Jianpeng
