RE: 2.6 device mapper performance?

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

then i run out of idea.

i guess only evms developer can tell u exactly why 2.6 evms has such
performance loss compared with 2.4.x

both evms and lvm use device mapper in kernel and i do not see such
performance loss in lvm. so pretty strange,

ming

On Wed, 2006-03-15 at 13:48 -0800, Ken Hwang wrote:
> Hi Ming,
> 
> I did blockdev --setra 1024 on kernel 2.6 system to make the same number as
> read from kernel 2.4 and the result:
> test:sync; time dd if=/dev/evms/volume1 of=/dev/null bs=1024k count=1024
> kernel 2.6 got 44.444s/0.004s/24.254s, and it was 46.690s/0.024s/26.902s.
> It's still far away from kernel 2.4: 33.649s/0.010s/20.430s.
> 
> 
> blockdev --setra 64 /dev/evms.nodes/md/md3
> test:sync; time dd if=/dev/evms/.nodes/md/md3 of=/dev/null bs=1024k
> count=1024
> kernel 2.6 got 26.770s/0.016s/11.257s, and it was 23.763s/0.008s/16.097s.
> The real time gets slower but system time gets faster. And they are still
> not close to
> kernel 2.4 19.471s/0.000s/13.480s
> 
> Do you have any advice I can do to tune the 2.6 performance?
> 
> Thanks in advance,
> 
> Ken
> 
> -----Original Message-----
> From: Ming Zhang [mailto:mingz@ele.uri.edu]
> Sent: Saturday, March 11, 2006 3:17 PM
> To: ken.hwang@zyxel.com
> Cc: device-mapper development
> Subject: RE: [dm-devel] 2.6 device mapper performance?
> 
> 
> 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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