Re: [PATCH 0/6][RFC] virtio-blk: Change I/O path from request to BIO

[Minchan Kim <minchan@kernel.org>]

Hi Sasha!

On Wed, Dec 21, 2011 at 10:28:52AM +0200, Sasha Levin wrote:
> On Wed, 2011-12-21 at 10:00 +0900, Minchan Kim wrote:
> > This patch is follow-up of Christohp Hellwig's work
> > [RFC: ->make_request support for virtio-blk].
> > http://thread.gmane.org/gmane.linux.kernel/1199763
> > 
> > Quote from hch
> > "This patchset allows the virtio-blk driver to support much higher IOP
> > rates which can be driven out of modern PCI-e flash devices.  At this
> > point it really is just a RFC due to various issues."
> > 
> > I fixed race bug and add batch I/O for enhancing sequential I/O,
> > FLUSH/FUA emulation.
> > 
> > I tested this patch on fusion I/O device by aio-stress.
> > Result is following as.
> > 
> > Benchmark : aio-stress (64 thread, test file size 512M, 8K io per IO, O_DIRECT write)
> > Environment: 8 socket - 8 core, 2533.372Hz, Fusion IO 320G storage
> > Test repeated by 20 times
> > Guest I/O scheduler : CFQ
> > Host I/O scheduler : NOOP
> > 
> >             Request            	BIO(patch 1-4)          BIO-batch(patch 1-6)
> >          (MB/s)  stddev 	(MB/s)  stddev  	(MB/s)  stddev
> > w        737.820 4.063  	613.735 31.605  	730.288 24.854
> > rw       208.754 20.450 	314.630 37.352  	317.831 41.719
> > r        770.974 2.340  	347.483 51.370  	750.324 8.280
> > rr       250.391 16.910 	350.053 29.986  	325.976 24.846
> > 
> > This patch enhances ramdom I/O performance compared to request-based I/O path.
> > It's still RFC so welcome to any comment and review.
> 
> I did a benchmark against a /dev/shm device instead of an actual storage
> to get rid of any artifacts which are caused by the storage itself, and
> saw that while there was a nice improvement across the board, the hit
> against sequential read and write was quite significant.

Hmm, it seems bandwidth test of sequential is bad but io test is still good.
I don't know how it is possbile that iops is better but bandwidth is bad.
Anyway, it seems sequential write bw is severe but I think it could be
better if test makes many lock overhead in vblk->lock because this patch
is started from the lock overhead.

Thanks for the testing, Sasha!

> 
> I ran the tests with fio running in KVM tool against a 2G file located
> in /dev/shm. Here is a summary of the results:
> 
> Before:
> write_iops_seq
>   write: io=1409.8MB, bw=144217KB/s, iops=36054 , runt= 10010msec
> write_bw_seq
>   write: io=7700.0MB, bw=1323.5MB/s, iops=1323 , runt=  5818msec
> read_iops_seq
>   read : io=1453.7MB, bw=148672KB/s, iops=37168 , runt= 10012msec
> read_bw_seq
>   read : io=7700.0MB, bw=1882.7MB/s, iops=1882 , runt=  4090msec
> write_iops_rand
>   write: io=1266.4MB, bw=129479KB/s, iops=32369 , runt= 10015msec
> write_bw_rand
>   write: io=7539.0MB, bw=1106.1MB/s, iops=1106 , runt=  6811msec
> read_iops_rand
>   read : io=1373.3MB, bw=140475KB/s, iops=35118 , runt= 10010msec
> read_bw_rand
>   read : io=7539.0MB, bw=1314.4MB/s, iops=1314 , runt=  5736msec
> readwrite_iops_seq
>   read : io=726172KB, bw=72292KB/s, iops=18072 , runt= 10045msec
>   write: io=726460KB, bw=72321KB/s, iops=18080 , runt= 10045msec
> readwrite_bw_seq
>   read : io=3856.0MB, bw=779574KB/s, iops=761 , runt=  5065msec
>   write: io=3844.0MB, bw=777148KB/s, iops=758 , runt=  5065msec
> readwrite_iops_rand
>   read : io=701780KB, bw=70094KB/s, iops=17523 , runt= 10012msec
>   write: io=706120KB, bw=70527KB/s, iops=17631 , runt= 10012msec
> readwrite_bw_rand
>   read : io=3705.0MB, bw=601446KB/s, iops=587 , runt=  6308msec
>   write: io=3834.0MB, bw=622387KB/s, iops=607 , runt=  6308msec
> 
> After:
> write_iops_seq
>   write: io=1591.4MB, bw=162626KB/s, iops=40656 , runt= 10020msec
> write_bw_seq
>   write: io=7700.0MB, bw=1276.4MB/s, iops=1276 , runt=  6033msec
> read_iops_seq
>   read : io=1615.7MB, bw=164680KB/s, iops=41170 , runt= 10046msec
> read_bw_seq
>   read : io=7700.0MB, bw=1407.1MB/s, iops=1407 , runt=  5469msec
> write_iops_rand
>   write: io=1243.1MB, bw=126304KB/s, iops=31575 , runt= 10085msec
> write_bw_rand
>   write: io=7539.0MB, bw=1206.3MB/s, iops=1206 , runt=  6250msec
> read_iops_rand
>   read : io=1533.1MB, bw=156795KB/s, iops=39198 , runt= 10018msec
> read_bw_rand
>   read : io=7539.0MB, bw=1413.7MB/s, iops=1413 , runt=  5333msec
> readwrite_iops_seq
>   read : io=819124KB, bw=81790KB/s, iops=20447 , runt= 10015msec
>   write: io=823136KB, bw=82190KB/s, iops=20547 , runt= 10015msec
> readwrite_bw_seq
>   read : io=3913.0MB, bw=704946KB/s, iops=688 , runt=  5684msec
>   write: io=3787.0MB, bw=682246KB/s, iops=666 , runt=  5684msec
> readwrite_iops_rand
>   read : io=802148KB, bw=80159KB/s, iops=20039 , runt= 10007msec
>   write: io=801192KB, bw=80063KB/s, iops=20015 , runt= 10007msec
> readwrite_bw_rand
>   read : io=3731.0MB, bw=677762KB/s, iops=661 , runt=  5637msec
>   write: io=3808.0MB, bw=691750KB/s, iops=675 , runt=  5637msec
> 
> -- 
> 
> Sasha.
> 
> 

-- 
Kind regards,
Minchan Kim