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. NeilBrown
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