RE: 2.6 device mapper performance?

[Ming Zhang <mingz@ele.uri.edu>]

On Fri, 2006-03-10 at 21:58 -0800, Ken Hwang wrote:
> Hi Ming,
> 
> I did more tests and list them at the following. Please help me analyze them
> if it's possible and thanks. Allow me describe the disk/volume layout. I had
> 4 120GB sata disks as sda, sdb, sdc, sdd. And they form 4 raid5 region, on
> top of the raid5 region there is a container, then I take 50% of the
> container to be a evms region, and then put a evms volume /dev/evms/volume1
> on top of the region. And I believe the raid5 region I used can be found at
> /dev/evms/.nodes/md/md3.
> 
> test: sync; time dd if=/dev/evms/volume1 of=/dev/null bs=1024k count=1024
> kernel 2.4 got 33.649s/0.010s/20.430s (real/user/sys)
> kernel 2.6 got 46.690s/0.024s/26.902s
> 
> test: sync; time dd if=/dev/evms/.nodes/md/md3 of=/dev/null bs=1024k
> count=1024
> kernel 2.4: 19.471s/0.000s/13.480s
> kernel 2.6: 23.763s/0.008s/16.097s
> 
> test: sync; time dd if=/dev/zero of=/dev/evms/volume1 bs=1024k count=1024
> kernel 2.4: 69.183s/0.000s/15.430s
> krenel 2.6: 52.543s/0.004/7.640s
> 
> test: sync; time dd if=/dev/zero of=/dev/evms/.nodes/md/md3 bs=1024k
> count=1024
> kernel 2.4: 37.862s/0.000s/11.730s
> kernel 2.6: 23.628s/0.000s/5.536s
> 
> test: blockdev --getra /dev/evms/volume1
> kernel 2.4: 1024
> kernel 2.6: 384

try to increase this number by --setra with blockdev

> 
> test: blockdev --getra /dev/evms/.nodes/md/md3
> kernel 2.4: 64
> kernel 2.6: 256
> 
> Looks like kernel 2.4 reading is faster than 2.6 but 2.6 writing is faster.
> 
> By comparing read from md3 and volume1,
> kernel 2.4 drop from 19.471s to 33.649s (72.8%)
> kernel 2.6 drop from 23.763s to 46.690s (96.4%)
> 
> By comparing write to md3 and volume1,
> kernel 2.4 drop from 37.862s to 69.183s (82.7%)
> kernel 2.6 drop from 23.628s to 52.543s (122.4%)
> 
> What's the blockdev numbers mean?

yes, pretty big drop here. no idea why. i think both lvm and evms use dm
and should not have such big difference.

that is to query/set the readahead buffer window, useful for sequential
workload.


> 
> Thanks,
> 
> Ken
> 
> 
> -----Original Message-----
> From: Ming Zhang [mailto:mingz@ele.uri.edu]
> Sent: Friday, March 10, 2006 8:59 AM
> To: ken.hwang@zyxel.com; device-mapper development
> Subject: Re: [dm-devel] 2.6 device mapper performance?
> 
> 
> u have too many chances here. so hard to blame any one. suggest u to
> test it one by one if possible.
> 
> for example, have same box run 2.4 and 2.6, test performance on volume
> first before run xfs, and samba.
> 
> ming
> 
> On Wed, 2006-03-08 at 16:49 -0800, Ken Hwang wrote:
> > Hi,
> >
> > I'm not sure I should ask this question here, if this is not the place
> then
> > I apologize. I have a home made NAS with Linux. I use evms to create
> volume,
> > put xfs on top of it, and then use samba to share it with Windows clients.
> > When I was using kernel 2.4 with all the needed patches I could get
> netbench
> > 106Mbps with 4 clients, and 95Mbps with 8 clients. Recently I upgraded the
> > same hardware to kernel 2.6 (I also upgraded the related application such
> as
> > samba, xfs utility, and dmsetup accordingly). Then I ran netbench again
> and
> > got 80Mbps with 4 clients, 53Mbps with 8 clients. Which drop almost 80%
> (95
> > vs 53) in 8 clients case.
> >
> > I then  make and mount xfs on another raid5 (which uses the same disk but
> on
> > different partitions) and found it got better performance (95Mbps with 4
> > clients, 85Mbps with 8 clients). In brief:
> > xfs volume on raid5 md/md1 on sda6/sdb6/sdc6/sdd6 netbench: 95/85Mbps
> > xfs volume on EVMS volume /dev/evms/volume1 on raid5 md/md3 on
> > sda8/sdb8/sdc8/sdd8: 80/53Mbps
> >
> > Do you think the slow down (85 to 53Mbps) was caused by device mapper?
> > Please advice.
> >
> > Ken
> >
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