It's seem that the limit is mainly going in high queue depth (+- > 16)
Here the result in iops with 1client- 4krandread- 3osd - with differents queue depth size.
rbd_cache is almost the same than without cache with queue depth <16
cache
-----
qd1: 1651
qd2: 3482
qd4: 7958
qd8: 17912
qd16: 36020
qd32: 42765
qd64: 46169
no cache
--------
qd1: 1748
qd2: 3570
qd4: 8356
qd8: 17732
qd16: 41396
qd32: 78633
qd64: 79063
qd128: 79550
----- Mail original -----
De: "aderumier" <aderumier@xxxxxxxxx>
À: "pushpesh sharma" <pushpesh.eck@xxxxxxxxx>
Cc: "ceph-devel" <ceph-devel@xxxxxxxxxxxxxxx>, "ceph-users" <ceph-users@xxxxxxxxxxxxxx>
Envoyé: Mardi 9 Juin 2015 09:28:21
Objet: Re: rbd_cache, limiting read on high iops around 40k
Hi,
We tried adding more RBDs to single VM, but no luck.
If you want to scale with more disks in a single qemu vm, you need to use iothread feature from qemu and assign 1 iothread by disk (works with virtio-blk).
It's working for me, I can scale with adding more disks.
My bench here are done with fio-rbd on host.
I can scale up to 400k iops with 10clients-rbd_cache=off on a single host and around 250kiops 10clients-rbdcache=on.
I just wonder why I don't have performance decrease around 30k iops with 1osd.
I'm going to see if this tracker
http://tracker.ceph.com/issues/11056
could be the cause.
(My master build was done some week ago)
----- Mail original -----
De: "pushpesh sharma" <pushpesh.eck@xxxxxxxxx>
À: "aderumier" <aderumier@xxxxxxxxx>
Cc: "ceph-devel" <ceph-devel@xxxxxxxxxxxxxxx>, "ceph-users" <ceph-users@xxxxxxxxxxxxxx>
Envoyé: Mardi 9 Juin 2015 09:21:04
Objet: Re: rbd_cache, limiting read on high iops around 40k
Hi Alexandre,
We have also seen something very similar on Hammer(0.94-1). We were doing some benchmarking for VMs hosted on hypervisor (QEMU-KVM, openstack-juno). Each Ubuntu-VM has a RBD as root disk, and 1 RBD as additional storage. For some strange reason it was not able to scale 4K- RR iops on each VM beyond 35-40k. We tried adding more RBDs to single VM, but no luck. However increasing number of VMs to 4 on a single hypervisor did scale to some extent. After this there was no much benefit we got from adding more VMs.
Here is the trend we have seen, x-axis is number of hypervisor, each hypervisor has 4 VM, each VM has 1 RBD:-
VDbench is used as benchmarking tool. We were not saturating network and CPUs at OSD nodes. We were not able to saturate CPUs at hypervisors, and that is where we were suspecting of some throttling effect. However we haven't setted any such limits from nova or kvm end. We tried some CPU pinning and other KVM related tuning as well, but no luck.
We tried the same experiment on a bare metal. It was 4K RR IOPs were scaling from 40K(1 RBD) to 180K(4 RBDs). But after that rather than scaling beyond that point the numbers were actually degrading. (Single pipe more congestion effect)
We never suspected that rbd cache enable could be detrimental to performance. It would nice to route cause the problem if that is the case.
On Tue, Jun 9, 2015 at 11:21 AM, Alexandre DERUMIER < aderumier@xxxxxxxxx > wrote:
Hi,
I'm doing benchmark (ceph master branch), with randread 4k qdepth=32,
and rbd_cache=true seem to limit the iops around 40k
no cache
--------
1 client - rbd_cache=false - 1osd : 38300 iops
1 client - rbd_cache=false - 2osd : 69073 iops
1 client - rbd_cache=false - 3osd : 78292 iops
cache
-----
1 client - rbd_cache=true - 1osd : 38100 iops
1 client - rbd_cache=true - 2osd : 42457 iops
1 client - rbd_cache=true - 3osd : 45823 iops
Is it expected ?
fio result rbd_cache=false 3 osd
--------------------------------
rbd_iodepth32-test: (g=0): rw=randread, bs=4K-4K/4K-4K/4K-4K, ioengine=rbd, iodepth=32
fio-2.1.11
Starting 1 process
rbd engine: RBD version: 0.1.9
Jobs: 1 (f=1): [r(1)] [100.0% done] [307.5MB/0KB/0KB /s] [78.8K/0/0 iops] [eta 00m:00s]
rbd_iodepth32-test: (groupid=0, jobs=1): err= 0: pid=113548: Tue Jun 9 07:48:42 2015
read : io=10000MB, bw=313169KB/s, iops=78292, runt= 32698msec
slat (usec): min=5, max=530, avg=11.77, stdev= 6.77
clat (usec): min=70, max=2240, avg=336.08, stdev=94.82
lat (usec): min=101, max=2247, avg=347.84, stdev=95.49
clat percentiles (usec):
| 1.00th=[ 173], 5.00th=[ 209], 10.00th=[ 231], 20.00th=[ 262],
| 30.00th=[ 282], 40.00th=[ 302], 50.00th=[ 322], 60.00th=[ 346],
| 70.00th=[ 370], 80.00th=[ 402], 90.00th=[ 454], 95.00th=[ 506],
| 99.00th=[ 628], 99.50th=[ 692], 99.90th=[ 860], 99.95th=[ 948],
| 99.99th=[ 1176]
bw (KB /s): min=238856, max=360448, per=100.00%, avg=313402.34, stdev=25196.21
lat (usec) : 100=0.01%, 250=15.94%, 500=78.60%, 750=5.19%, 1000=0.23%
lat (msec) : 2=0.03%, 4=0.01%
cpu : usr=74.48%, sys=13.25%, ctx=703225, majf=0, minf=12452
IO depths : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.8%, 16=87.0%, 32=12.1%, >=64=0.0%
submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
complete : 0=0.0%, 4=91.6%, 8=3.4%, 16=4.5%, 32=0.4%, 64=0.0%, >=64=0.0%
issued : total=r=2560000/w=0/d=0, short=r=0/w=0/d=0
latency : target=0, window=0, percentile=100.00%, depth=32
Run status group 0 (all jobs):
READ: io=10000MB, aggrb=313169KB/s, minb=313169KB/s, maxb=313169KB/s, mint=32698msec, maxt=32698msec
Disk stats (read/write):
dm-0: ios=0/45, merge=0/0, ticks=0/0, in_queue=0, util=0.00%, aggrios=0/24, aggrmerge=0/21, aggrticks=0/0, aggrin_queue=0, aggrutil=0.00%
sda: ios=0/24, merge=0/21, ticks=0/0, in_queue=0, util=0.00%
fio result rbd_cache=true 3osd
------------------------------
rbd_iodepth32-test: (g=0): rw=randread, bs=4K-4K/4K-4K/4K-4K, ioengine=rbd, iodepth=32
fio-2.1.11
Starting 1 process
rbd engine: RBD version: 0.1.9
Jobs: 1 (f=1): [r(1)] [100.0% done] [171.6MB/0KB/0KB /s] [43.1K/0/0 iops] [eta 00m:00s]
rbd_iodepth32-test: (groupid=0, jobs=1): err= 0: pid=113389: Tue Jun 9 07:47:30 2015
read : io=10000MB, bw=183296KB/s, iops=45823, runt= 55866msec
slat (usec): min=7, max=805, avg=21.26, stdev=15.84
clat (usec): min=101, max=4602, avg=478.55, stdev=143.73
lat (usec): min=123, max=4669, avg=499.80, stdev=146.03
clat percentiles (usec):
| 1.00th=[ 227], 5.00th=[ 274], 10.00th=[ 306], 20.00th=[ 350],
| 30.00th=[ 390], 40.00th=[ 430], 50.00th=[ 470], 60.00th=[ 506],
| 70.00th=[ 548], 80.00th=[ 596], 90.00th=[ 660], 95.00th=[ 724],
| 99.00th=[ 844], 99.50th=[ 908], 99.90th=[ 1112], 99.95th=[ 1288],
| 99.99th=[ 2192]
bw (KB /s): min=115280, max=204416, per=100.00%, avg=183315.10, stdev=15079.93
lat (usec) : 250=2.42%, 500=55.61%, 750=38.48%, 1000=3.28%
lat (msec) : 2=0.19%, 4=0.01%, 10=0.01%
cpu : usr=60.27%, sys=12.01%, ctx=2995393, majf=0, minf=14100
IO depths : 1=0.1%, 2=0.1%, 4=0.2%, 8=13.5%, 16=81.0%, 32=5.3%, >=64=0.0%
submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
complete : 0=0.0%, 4=95.0%, 8=0.1%, 16=1.0%, 32=4.0%, 64=0.0%, >=64=0.0%
issued : total=r=2560000/w=0/d=0, short=r=0/w=0/d=0
latency : target=0, window=0, percentile=100.00%, depth=32
Run status group 0 (all jobs):
READ: io=10000MB, aggrb=183295KB/s, minb=183295KB/s, maxb=183295KB/s, mint=55866msec, maxt=55866msec
Disk stats (read/write):
dm-0: ios=0/61, merge=0/0, ticks=0/8, in_queue=8, util=0.01%, aggrios=0/29, aggrmerge=0/32, aggrticks=0/8, aggrin_queue=8, aggrutil=0.01%
sda: ios=0/29, merge=0/32, ticks=0/8, in_queue=8, util=0.01%
