On Fri, 24 Aug 2012 12:21:30 +0800 kedacomkernel <kedacomkernel@xxxxxxxxx> wrote: > On 2012-08-24 11:12 Shaohua Li <shli@xxxxxxxxxx> Wrote: > >2012/8/23 Jianpeng Ma <majianpeng@xxxxxxxxx>: > >> On 2012-08-23 15:55 Shaohua Li <shli@xxxxxxxxxx> Wrote: > >>>2012/8/23 Jianpeng Ma <majianpeng@xxxxxxxxx>: > >>>> On 2012-08-23 14:08 Shaohua Li <shli@xxxxxxxxxx> Wrote: > >>>>>2012/8/16 Shaohua Li <shli@xxxxxxxxxx>: > >>>>>> 2012/8/16 Jianpeng Ma <majianpeng@xxxxxxxxx>: > >>>>>>> On 2012-08-15 09:44 Shaohua Li <shli@xxxxxxxxxx> Wrote: > >>>>>>>>On Wed, Aug 15, 2012 at 10:56:10AM +1000, NeilBrown wrote: > >>>>>>>>> On Tue, 14 Aug 2012 14:33:43 +0800 Shaohua Li <shli@xxxxxxxxxx> wrote: > >>>>>>>>> > >>>>>>>>> > On Thu, Aug 09, 2012 at 01:07:01PM +0800, Shaohua Li wrote: > >>>>>>>>> > > 2012/8/9 NeilBrown <neilb@xxxxxxx>: > >>>>>>>>> > > > On Thu, 9 Aug 2012 09:20:05 +0800 "Jianpeng Ma" <majianpeng@xxxxxxxxx> wrote: > >>>>>>>>> > > > > >>>>>>>>> > > >> On 2012-08-08 20:53 Shaohua Li <shli@xxxxxxxxxx> Wrote: > >>>>>>>>> > > >> >2012/8/8 Jianpeng Ma <majianpeng@xxxxxxxxx>: > >>>>>>>>> > > >> >> On 2012-08-08 10:58 Shaohua Li <shli@xxxxxxxxxx> Wrote: > >>>>>>>>> > > >> >>>2012/8/7 Jianpeng Ma <majianpeng@xxxxxxxxx>: > >>>>>>>>> > > >> >>>> On 2012-08-07 13:32 Shaohua Li <shli@xxxxxxxxxx> Wrote: > >>>>>>>>> > > >> >>>>>2012/8/7 Jianpeng Ma <majianpeng@xxxxxxxxx>: > >>>>>>>>> > > >> >>>>>> On 2012-08-07 11:22 Shaohua Li <shli@xxxxxxxxxx> Wrote: > >>>>>>>>> > > >> >>>>>>>My directIO randomwrite 4k workload shows a 10~20% regression caused by commit > >>>>>>>>> > > >> >>>>>>>895e3c5c58a80bb. directIO usually is random IO and if request size isn't big > >>>>>>>>> > > >> >>>>>>>(which is the common case), delay handling of the stripe hasn't any advantages. > >>>>>>>>> > > >> >>>>>>>For big size request, delay can still reduce IO. > >>>>>>>>> > > >> >>>>>>> > >>>>>>>>> > > >> >>>>>>>Signed-off-by: Shaohua Li <shli@xxxxxxxxxxxx> > >>>>>>>>> > > >> >>>> [snip] > >>>>>>>>> > > >> >>>>>>>-- > >>>>>>>>> > > >> >>>>>> May be used size to judge is not a good method. > >>>>>>>>> > > >> >>>>>> I firstly sended this patch, only want to control direct-write-block,not for reqular file. > >>>>>>>>> > > >> >>>>>> Because i think if someone used direct-write-block for raid5,he should know the feature of raid5 and he can control > >>>>>>>>> > > >> >>>>>> for write to full-write. > >>>>>>>>> > > >> >>>>>> But at that time, i did know how to differentiate between regular file and block-device. > >>>>>>>>> > > >> >>>>>> I thik we should do something to do this. > >>>>>>>>> > > >> >>>>> > >>>>>>>>> > > >> >>>>>I don't think it's possible user can control his write to be a > >>>>>>>>> > > >> >>>>>full-write even for > >>>>>>>>> > > >> >>>>>raw disk IO. Why regular file and block device io matters here? > >>>>>>>>> > > >> >>>>> > >>>>>>>>> > > >> >>>>>Thanks, > >>>>>>>>> > > >> >>>>>Shaohua > >>>>>>>>> > > >> >>>> Another problem is the size. How to judge the size is large or not? > >>>>>>>>> > > >> >>>> A syscall write is a dio and a dio may be split more bios. > >>>>>>>>> > > >> >>>> For my workload, i usualy write chunk-size. > >>>>>>>>> > > >> >>>> But your patch is judge by bio-size. > >>>>>>>>> > > >> >>> > >>>>>>>>> > > >> >>>I'd ignore workload which does sequential directIO, though > >>>>>>>>> > > >> >>>your workload is, but I bet no real workloads are. So I'd like > >>>>>>>>> > > >> >> Sorry,my explain maybe not corcrect. I write data once which size is almost chunks-size * devices,in order to full-write > >>>>>>>>> > > >> >> and as possible as to no pre-read operation. > >>>>>>>>> > > >> >>>only to consider big size random directio. I agree the size > >>>>>>>>> > > >> >>>judge is arbitrary. I can optimize it to be only consider stripe > >>>>>>>>> > > >> >>>which hits two or more disks in one bio, but not sure if it's > >>>>>>>>> > > >> >>>worthy doing. Not ware big size directio is common, and even > >>>>>>>>> > > >> >>>is, big size request IOPS is low, a bit delay maybe not a big > >>>>>>>>> > > >> >>>deal. > >>>>>>>>> > > >> >> If add a acc_time for 'striep_head' to control? > >>>>>>>>> > > >> >> When get_active_stripe() is ok, update acc_time. > >>>>>>>>> > > >> >> For some time, stripe_head did not access and it shold pre-read. > >>>>>>>>> > > >> > > >>>>>>>>> > > >> >Do you want to add a timer for each stripe? This is even ugly. > >>>>>>>>> > > >> >How do you choose the expire time? A time works for harddisk > >>>>>>>>> > > >> >definitely will not work for a fast SSD. > >>>>>>>>> > > >> A time is like the size which is arbitrary. > >>>>>>>>> > > >> How about add a interface in sysfs to control by user? > >>>>>>>>> > > >> Only user can judge the workload, which sequatial write or random write. > >>>>>>>>> > > > > >>>>>>>>> > > > This is getting worse by the minute. A sysfs interface for this is > >>>>>>>>> > > > definitely not a good idea. > >>>>>>>>> > > > > >>>>>>>>> > > > The REQ_NOIDLE flag is a pretty clear statement that no more requests that > >>>>>>>>> > > > merge with this one are expected. If some use cases sends random requests, > >>>>>>>>> > > > maybe it should be setting REQ_NOIDLE. > >>>>>>>>> > > > > >>>>>>>>> > > > Maybe someone should do some research and find out why WRITE_ODIRECT doesn't > >>>>>>>>> > > > include REQ_NOIDLE. Understanding that would help understand the current > >>>>>>>>> > > > problem. > >>>>>>>>> > > > >>>>>>>>> > > A quick search shows only cfq-iosched uses REQ_NOIDLE. In > >>>>>>>>> > > cfq, a queue is idled to avoid losing its share. REQ_NOIDLE > >>>>>>>>> > > tells cfq to avoid idle, since the task will not dispatch further > >>>>>>>>> > > requests any more. Note this isn't no merge. > >>>>>>>>> > > >>>>>>>>> > Since REQ_NOIDLE has no relationship with request merge, we'd better remove it. > >>>>>>>>> > I came out a new patch, which doesn't depend on request size any more. With > >>>>>>>>> > this patch, sequential directio will still introduce unnecessary raid5 preread > >>>>>>>>> > (especially for small size IO), but I bet no app does sequential small size > >>>>>>>>> > directIO. > >>>>>>>>> > > >>>>>>>>> > Thanks, > >>>>>>>>> > Shaohua > >>>>>>>>> > > >>>>>>>>> > Subject: raid5: fix directio regression > >>>>>>>>> > > >>>>>>>>> > My directIO randomwrite 4k workload shows a 10~20% regression caused by commit > >>>>>>>>> > 895e3c5c58a80bb. This commit isn't friendly for small size random IO, because > >>>>>>>>> > delaying such request hasn't any advantages. > >>>>>>>>> > > >>>>>>>>> > DirectIO usually is random IO. I thought we can ignore request merge between > >>>>>>>>> > bios from different io_submit. So we only consider one bio which can drive > >>>>>>>>> > unnecessary preread in raid5, which is large request. If a bio is large enough > >>>>>>>>> > and some of its stripes will access two or more disks, such stripes should be > >>>>>>>>> > delayed to avoid unnecessary preread till bio for the last disk of the strips > >>>>>>>>> > is added. > >>>>>>>>> > > >>>>>>>>> > REQ_NOIDLE doesn't mean about request merge, I deleted it. > >>>>>>>>> > >>>>>>>>> Hi, > >>>>>>>>> Have you tested what effect this has on large sequential direct writes? > >>>>>>>>> Because it don't make sense to me and I would be surprised if it improves > >>>>>>>>> things. > >>>>>>>>> > >>>>>>>>> You are delaying setting the STRIPE_PREREAD_ACTIVE bit until you think you > >>>>>>>>> have submitted all the writes from this bio that apply to the give stripe. > >>>>>>>>> That does make some sense, however it doesn't seem to deal with the > >>>>>>>>> possibility that the one bio covers parts of two different stripes. In that > >>>>>>>>> case the first stripe never gets STRIPE_PREREAD_ACTIVE set, so it is delayed > >>>>>>>>> despite having 'REQ_SYNC' set. > >>>>>>>> > >>>>>>>>I didn't get your point. Isn't last_sector - logical_sector < chunk_sectors true > >>>>>>>>in the case? > >>>>>>>> > >>>>>>>>> Also, and more significantly, plugging should mean that the various > >>>>>>>>> stripe_heads are not even looked at until all of the original bio is > >>>>>>>>> processed, so while STRIPE_PREREAD_ACTIVE might get set early, it should not > >>>>>>>>> get processed until the whole bio is processed and the queue is unplugged. > >>>>>>>>> > >>>>>>>>> So I don't think this patch should make a difference on large direct writes, > >>>>>>>>> and if it does then something strange is going on that I'd like to > >>>>>>>>> understand first. > >>>>>>>> > >>>>>>>>Aha, ok, this makes sense. recent delayed stripe release should make the > >>>>>>>>problem go away. So Jianpeng, can you try your workload with the commit > >>>>>>>>reverted with a recent kernel please? > >>>>>>>> > >>>>>>> I tested used your patch in my workload. > >>>>>>> Like the neil said, the performance does not regress. > >>>>>>> But if the code is : > >>>>>>>> if (test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) > >>>>>>>> release_stripe(sh); > >>>>>>>> else > >>>>>>>> release_stripe_plug(mddev, sh); > >>>>>>> The speed is about 76MB/s.With those code the speed is 200MB/s. > >>>>>> > >>>>>> Hmm, what I want to test is upstream kernel with commit 895e3c5c58a80bb > >>>>>> reverted. don't apply my patch. We want to just revert the commit. > >>>>> > >>>>>Did you have data for your original workload with 895e3c5c58a80bb > >>>>>reverted now? > >>>> our raid5 which had 14 SATA HDDs. > >>>> > >>>> with 895e3c5c58a80bb reverted: > >>>> using dd to test 55MB/s > >>>> using our-fs 200-250Mb/s > >>>> > >>>> with 895e3c5c58a80bb: > >>>> using dd to test 275MB/s > >>>> using our-fs 500-550Mb/s > >>> > >>>what's block size of dd in this test? In your original test, your > >>>BS covers chunk_sector*data_disks. In that case, > >>>895e3c5c58a80bb is likely not required. > >>> > >> With latest kernel(3.6-rc3), w/ or w/o 895e3c5c58a80bb, the result is the same. > >> The block size of dd is chunk_sector * data_disks. > >> Your patch(8811b5968f6216e97) is good. > >> I think it shoul revert 8811b5968f6216e97. > > > >revert 895e3c5c58a80bb, right? > yes. Because the 8811b5968f6216e97, it can revert. Thanks. I've reverted 895e3c5c58a80bb and will submit to -next later today. NeilBrown
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