Ryo Tsuruta wrote: > Hi Li, > > From: Ryo Tsuruta <ryov@xxxxxxxxxxxxx> > Subject: Re: [RFC PATCH dm-ioband] Added in blktrace msgs for dm-ioband > Date: Thu, 07 May 2009 09:23:22 +0900 (JST) > >> Hi Li, >> >> From: Li Zefan <lizf@xxxxxxxxxxxxxx> >> Subject: Re: [RFC PATCH dm-ioband] Added in blktrace msgs for dm-ioband >> Date: Mon, 04 May 2009 11:24:27 +0800 >> >>> Ryo Tsuruta wrote: >>>> Hi Alan, >>>> >>>>> Hi Ryo - >>>>> >>>>> I don't know if you are taking in patches, but whilst trying to uncover >>>>> some odd behavior I added some blktrace messages to dm-ioband-ctl.c. If >>>>> you're keeping one code base for old stuff (2.6.18-ish RHEL stuff) and >>>>> upstream you'll have to #if around these (the blktrace message stuff >>>>> came in around 2.6.26 or 27 I think). >>>>> >>>>> My test case was to take a single 400GB storage device, put two 200GB >>>>> partitions on it and then see what the "penalty" or overhead for adding >>>>> dm-ioband on top. To do this I simply created an ext2 FS on each >>>>> partition in parallel (two processes each doing a mkfs to one of the >>>>> partitions). Then I put two dm-ioband devices on top of the two >>>>> partitions (setting the weight to 100 in both cases - thus they should >>>>> have equal access). >>>>> >>>>> Using default values I was seeing /very/ large differences - on the >>>>> order of 3X. When I bumped the number of tokens to a large number >>>>> (10,240) the timings got much closer (<2%). I have found that using >>>>> weight-iosize performs worse than weight (closer to 5% penalty). >>>> I could reproduce similar results. One dm-ioband device seems to stop >>>> issuing I/Os for a few seconds at times. I'll investigate more on that. >>>> >>>>> I'll try to formalize these results as I go forward and report out on >>>>> them. In any event, I thought I'd share this patch with you if you are >>>>> interested... >>>> Thanks. I'll include your patche into the next release. >>>> >>> IMO we should use TRACE_EVENT instead of adding new blk_add_trace_msg(). >> Thanks for your suggestion. I'll use TRACE_EVENT instead. > > blk_add_trace_msg() supports both blktrace and tracepoints. I can > get messages from dm-ioband through debugfs. Could you expain why > should we use TRACE_EVENT instead? > Actually blk_add_trace_msg() has nothing to do with tracepoints.. If we use blk_add_trace_msg() is dm, we can use it in md, various block drivers and even ext4. So the right thing is, if a subsystem wants to add trace facility, it should use tracepoints/TRACE_EVENT. With TRACE_EVENT, you can get output through debugfs too, and it can be used together with blktrace: # echo 1 > /sys/block/dm/trace/enable # echo blk > /debugfs/tracing/current_tracer # echo dm-ioband-foo > /debugfs/tracing/tracing/set_event # cat /deubgfs/tracing/trace_pipe And you can enable dm-ioband-foo while disabling dm-ioband-bar, and you can use filter feature too. >>>>> Here's a sampling from some blktrace output (sorry for the wrapping) - I >>>>> should note that I'm a bit scared to see such large numbers of holds >>>>> going on when the token count should be >5,000 for each device... >>>>> Holding these back in an equal access situation is inhibiting the block >>>>> I/O layer to merge (most) of these (as mkfs performs lots & lots of >>>>> small but sequential I/Os). >> Thanks, >> Ryo Tsuruta > > Thanks, > Ryo Tsuruta > -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
