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? > > > > >> 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
