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? -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
