Is there a thread on the mailing list (or LKML?) with some background about tcp_low_latency and TCP_NODELAY?
BillOn Fri, Sep 11, 2015 at 2:30 AM, Jan Schermer <jan@xxxxxxxxxxx> wrote:
Can you try
echo 1 > /proc/sys/net/ipv4/tcp_low_latency
And see if it improves things? I remember there being an option to disable nagle completely, but it's gone apparently.
Jan
> On 11 Sep 2015, at 10:43, Nick Fisk <nick@xxxxxxxxxx> wrote:
>
>
>
>
>
>> -----Original Message-----
>> From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of
>> Somnath Roy
>> Sent: 11 September 2015 06:23
>> To: Rafael Lopez <rafael.lopez@xxxxxxxxxx>
>> Cc: ceph-users@xxxxxxxxxxxxxx
>> Subject: Re: bad perf for librbd vs krbd using FIO
>>
>> That’s probably because the krbd version you are using doesn’t have the
>> TCP_NODELAY patch. We have submitted it (and you can build it from latest
>> rbd source) , but, I am not sure when it will be in linux mainline.
>
> From memory it landed in 3.19, but there are also several issues with max IO size, max nr_requests and readahead. I would suggest for testing, try one of these:-
>
> http://gitbuilder.ceph.com/kernel-deb-precise-x86_64-basic/ref/ra-bring-back/
>
>
>>
>> Thanks & Regards
>> Somnath
>>
>> From: Rafael Lopez [mailto:rafael.lopez@xxxxxxxxxx]
>> Sent: Thursday, September 10, 2015 10:12 PM
>> To: Somnath Roy
>> Cc: ceph-users@xxxxxxxxxxxxxx
>> Subject: Re: bad perf for librbd vs krbd using FIO
>>
>> Ok I ran the two tests again with direct=1, smaller block size (4k) and smaller
>> total io (100m), disabled cache at ceph.conf side on client by adding:
>>
>> [client]
>> rbd cache = false
>> rbd cache max dirty = 0
>> rbd cache size = 0
>> rbd cache target dirty = 0
>>
>>
>> The result seems to have swapped around, now the librbd job is running
>> ~50% faster than the krbd job!
>>
>> ####### krbd job:
>>
>> [root@rcprsdc1r72-01-ac rafaell]# fio ext4_test
>> job1: (g=0): rw=rw, bs=4K-4K/4K-4K/4K-4K, ioengine=sync, iodepth=16
>> fio-2.2.8
>> Starting 1 process
>> Jobs: 1 (f=1): [W(1)] [100.0% done] [0KB/571KB/0KB /s] [0/142/0 iops] [eta
>> 00m:00s]
>> job1: (groupid=0, jobs=1): err= 0: pid=29095: Fri Sep 11 14:48:21 2015
>> write: io=102400KB, bw=647137B/s, iops=157, runt=162033msec
>> clat (msec): min=2, max=25, avg= 6.32, stdev= 1.21
>> lat (msec): min=2, max=25, avg= 6.32, stdev= 1.21
>> clat percentiles (usec):
>> | 1.00th=[ 2896], 5.00th=[ 4320], 10.00th=[ 4768], 20.00th=[ 5536],
>> | 30.00th=[ 5920], 40.00th=[ 6176], 50.00th=[ 6432], 60.00th=[ 6624],
>> | 70.00th=[ 6816], 80.00th=[ 7136], 90.00th=[ 7584], 95.00th=[ 7968],
>> | 99.00th=[ 9024], 99.50th=[ 9664], 99.90th=[15808], 99.95th=[17536],
>> | 99.99th=[19328]
>> bw (KB /s): min= 506, max= 1171, per=100.00%, avg=632.22, stdev=104.77
>> lat (msec) : 4=2.88%, 10=96.69%, 20=0.43%, 50=0.01%
>> cpu : usr=0.17%, sys=0.71%, ctx=25634, majf=0, minf=35
>> IO depths : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%,
>>> =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=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%,
>>> =64=0.0%
>> issued : total=r=0/w=25600/d=0, short=r=0/w=0/d=0,
>> drop=r=0/w=0/d=0
>> latency : target=0, window=0, percentile=100.00%, depth=16
>>
>> Run status group 0 (all jobs):
>> WRITE: io=102400KB, aggrb=631KB/s, minb=631KB/s, maxb=631KB/s,
>> mint=162033msec, maxt=162033msec
>>
>> Disk stats (read/write):
>> rbd0: ios=0/25638, merge=0/32, ticks=0/160765, in_queue=160745,
>> util=99.11%
>> [root@rcprsdc1r72-01-ac rafaell]#
>>
>> ###### librb job:
>>
>> [root@rcprsdc1r72-01-ac rafaell]# fio fio_rbd_test
>> job1: (g=0): rw=rw, bs=4K-4K/4K-4K/4K-4K, ioengine=rbd, iodepth=16
>> fio-2.2.8
>> Starting 1 process
>> rbd engine: RBD version: 0.1.9
>> Jobs: 1 (f=1): [W(1)] [100.0% done] [0KB/703KB/0KB /s] [0/175/0 iops] [eta
>> 00m:00s]
>> job1: (groupid=0, jobs=1): err= 0: pid=30568: Fri Sep 11 14:50:24 2015
>> write: io=102400KB, bw=950141B/s, iops=231, runt=110360msec
>> slat (usec): min=70, max=992, avg=115.05, stdev=30.07
>> clat (msec): min=13, max=117, avg=67.91, stdev=24.93
>> lat (msec): min=13, max=117, avg=68.03, stdev=24.93
>> clat percentiles (msec):
>> | 1.00th=[ 19], 5.00th=[ 26], 10.00th=[ 38], 20.00th=[ 40],
>> | 30.00th=[ 46], 40.00th=[ 62], 50.00th=[ 77], 60.00th=[ 85],
>> | 70.00th=[ 88], 80.00th=[ 91], 90.00th=[ 95], 95.00th=[ 99],
>> | 99.00th=[ 105], 99.50th=[ 110], 99.90th=[ 116], 99.95th=[ 117],
>> | 99.99th=[ 118]
>> bw (KB /s): min= 565, max= 3174, per=100.00%, avg=935.74, stdev=407.67
>> lat (msec) : 20=2.41%, 50=29.85%, 100=64.46%, 250=3.29%
>> cpu : usr=2.43%, sys=0.29%, ctx=7847, majf=0, minf=2750
>> IO depths : 1=6.2%, 2=12.5%, 4=25.0%, 8=50.0%, 16=6.2%, 32=0.0%,
>>> =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=94.1%, 8=0.0%, 16=5.9%, 32=0.0%, 64=0.0%,
>>> =64=0.0%
>> issued : total=r=0/w=25600/d=0, short=r=0/w=0/d=0,
>> drop=r=0/w=0/d=0
>> latency : target=0, window=0, percentile=100.00%, depth=16
>>
>> Run status group 0 (all jobs):
>> WRITE: io=102400KB, aggrb=927KB/s, minb=927KB/s, maxb=927KB/s,
>> mint=110360msec, maxt=110360msec
>>
>> Disk stats (read/write):
>> dm-1: ios=240/369, merge=0/0, ticks=742/40, in_queue=782, util=0.38%,
>> aggrios=240/379, aggrmerge=0/19, aggrticks=742/41, aggrin_queue=783,
>> aggrutil=0.39%
>> sda: ios=240/379, merge=0/19, ticks=742/41, in_queue=783, util=0.39%
>> [root@rcprsdc1r72-01-ac rafaell]#
>>
>>
>>
>> Confirmed speed (at least for krbd) using dd:
>> [root@rcprsdc1r72-01-ac rafaell]# dd if=/mnt/ssd/random100g
>> of=/mnt/rbd/dd_io_test bs=4k count=10000 oflag=direct
>> 10000+0 records in
>> 10000+0 records out
>> 40960000 bytes (41 MB) copied, 64.9799 s, 630 kB/s
>> [root@rcprsdc1r72-01-ac rafaell]#
>>
>>
>> Back to FIO, it's worse for 1M block size (librbd is about ~100% better perf).
>> 1M librbd:
>> Run status group 0 (all jobs):
>> WRITE: io=1024.0MB, aggrb=112641KB/s, minb=112641KB/s,
>> maxb=112641KB/s, mint=9309msec, maxt=9309msec
>>
>> 1M krbd:
>> Run status group 0 (all jobs):
>> WRITE: io=1024.0MB, aggrb=49939KB/s, minb=49939KB/s, maxb=49939KB/s,
>> mint=20997msec, maxt=20997msec
>>
>> Raf
>>
>> On 11 September 2015 at 14:33, Somnath Roy <Somnath.Roy@xxxxxxxxxxx>
>> wrote:
>> Only changing client side ceph.conf and rerunning the tests is sufficient.
>>
>> Thanks & Regards
>> Somnath
>>
>> From: Rafael Lopez [mailto:rafael.lopez@xxxxxxxxxx]
>> Sent: Thursday, September 10, 2015 8:58 PM
>> To: Somnath Roy
>> Cc: ceph-users@xxxxxxxxxxxxxx
>> Subject: Re: bad perf for librbd vs krbd using FIO
>>
>> Thanks for the quick reply Somnath, will give this a try.
>>
>> In order to set the rbd cache settings, is it a matter of updating the ceph.conf
>> file on the client only prior to running the test, or do I need to inject args to all
>> OSDs ?
>>
>> Raf
>>
>>
>> On 11 September 2015 at 13:39, Somnath Roy <Somnath.Roy@xxxxxxxxxxx>
>> wrote:
>> It may be due to rbd cache effect..
>> Try the following..
>>
>> Run your test with direct = 1 both the cases and rbd_cache = false (disable all
>> other rbd cache option as well). This should give you similar result like krbd.
>>
>> In direct =1 case, we saw ~10-20% degradation if we make rbd_cache = true.
>> But, direct = 0 case, it could be more as you are seeing..
>>
>> I think there is a delta (or need to tune properly) if you want to use rbd
>> cache.
>>
>> Thanks & Regards
>> Somnath
>>
>>
>>
>> From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of
>> Rafael Lopez
>> Sent: Thursday, September 10, 2015 8:24 PM
>> To: ceph-users@xxxxxxxxxxxxxx
>> Subject: bad perf for librbd vs krbd using FIO
>>
>> Hi all,
>>
>> I am seeing a big discrepancy between librbd and kRBD/ext4 performance
>> using FIO with single RBD image. RBD images are coming from same RBD
>> pool, same size and settings for both. The librbd results are quite bad by
>> comparison, and in addition if I scale up the kRBD FIO job with more
>> jobs/threads it increases up to 3-4x results below, but librbd doesn't seem to
>> scale much at all. I figured that it should be close to the kRBD result for a
>> single job/thread before parallelism comes into play though. RBD cache
>> settings are all default.
>>
>> I can see some obvious differences in FIO output, but not being well versed
>> with FIO I'm not sure what to make of it or where to start diagnosing the
>> discrepancy. Hunted around but haven't found anything useful, any
>> suggestions/insights would be appreciated.
>>
>> RBD cache settings:
>> [root@rcmktdc1r72-09-ac rafaell]# ceph --admin-daemon
>> /var/run/ceph/ceph-osd.659.asok config show | grep rbd_cache
>> "rbd_cache": "true",
>> "rbd_cache_writethrough_until_flush": "true",
>> "rbd_cache_size": "33554432",
>> "rbd_cache_max_dirty": "25165824",
>> "rbd_cache_target_dirty": "16777216",
>> "rbd_cache_max_dirty_age": "1",
>> "rbd_cache_max_dirty_object": "0",
>> "rbd_cache_block_writes_upfront": "false",
>> [root@rcmktdc1r72-09-ac rafaell]#
>>
>> This is the FIO job file for the kRBD job:
>>
>> [root@rcprsdc1r72-01-ac rafaell]# cat ext4_test
>> ; -- start job file --
>> [global]
>> rw=rw
>> size=100g
>> filename=/mnt/rbd/fio_test_file_ext4
>> rwmixread=0
>> rwmixwrite=100
>> percentage_random=0
>> bs=1024k
>> direct=0
>> iodepth=16
>> thread=1
>> numjobs=1
>> [job1]
>> ; -- end job file --
>>
>> [root@rcprsdc1r72-01-ac rafaell]#
>>
>> This is the FIO job file for the librbd job:
>>
>> [root@rcprsdc1r72-01-ac rafaell]# cat fio_rbd_test
>> ; -- start job file --
>> [global]
>> rw=rw
>> size=100g
>> rwmixread=0
>> rwmixwrite=100
>> percentage_random=0
>> bs=1024k
>> direct=0
>> iodepth=16
>> thread=1
>> numjobs=1
>> ioengine=rbd
>> rbdname=nas1-rds-stg31
>> pool=rbd
>> [job1]
>> ; -- end job file --
>>
>>
>> Here are the results:
>>
>> [root@rcprsdc1r72-01-ac rafaell]# fio ext4_test
>> job1: (g=0): rw=rw, bs=1M-1M/1M-1M/1M-1M, ioengine=sync, iodepth=16
>> fio-2.2.8
>> Starting 1 thread
>> job1: Laying out IO file(s) (1 file(s) / 102400MB)
>> Jobs: 1 (f=1): [W(1)] [100.0% done] [0KB/321.7MB/0KB /s] [0/321/0 iops] [eta
>> 00m:00s]
>> job1: (groupid=0, jobs=1): err= 0: pid=37981: Fri Sep 11 12:33:13 2015
>> write: io=102400MB, bw=399741KB/s, iops=390, runt=262314msec
>> clat (usec): min=411, max=574082, avg=2492.91, stdev=7316.96
>> lat (usec): min=418, max=574113, avg=2520.12, stdev=7318.53
>> clat percentiles (usec):
>> | 1.00th=[ 446], 5.00th=[ 458], 10.00th=[ 474], 20.00th=[ 510],
>> | 30.00th=[ 1064], 40.00th=[ 1096], 50.00th=[ 1160], 60.00th=[ 1320],
>> | 70.00th=[ 1592], 80.00th=[ 2448], 90.00th=[ 7712], 95.00th=[ 7904],
>> | 99.00th=[11072], 99.50th=[11712], 99.90th=[13120], 99.95th=[73216],
>> | 99.99th=[464896]
>> bw (KB /s): min= 264, max=2156544, per=100.00%, avg=412986.27,
>> stdev=375092.66
>> lat (usec) : 500=18.68%, 750=7.43%, 1000=2.11%
>> lat (msec) : 2=48.89%, 4=4.35%, 10=16.79%, 20=1.67%, 50=0.03%
>> lat (msec) : 100=0.03%, 250=0.02%, 500=0.01%, 750=0.01%
>> cpu : usr=1.24%, sys=45.38%, ctx=19298, majf=0, minf=974
>> IO depths : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%,
>>> =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=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%,
>>> =64=0.0%
>> issued : total=r=0/w=102400/d=0, short=r=0/w=0/d=0,
>> drop=r=0/w=0/d=0
>> latency : target=0, window=0, percentile=100.00%, depth=16
>>
>> Run status group 0 (all jobs):
>> WRITE: io=102400MB, aggrb=399740KB/s, minb=399740KB/s,
>> maxb=399740KB/s, mint=262314msec, maxt=262314msec
>>
>> Disk stats (read/write):
>> rbd0: ios=0/150890, merge=0/49, ticks=0/36117700, in_queue=36145277,
>> util=96.97%
>> [root@rcprsdc1r72-01-ac rafaell]#
>>
>> [root@rcprsdc1r72-01-ac rafaell]# fio fio_rbd_test
>> job1: (g=0): rw=rw, bs=1M-1M/1M-1M/1M-1M, ioengine=rbd, iodepth=16
>> fio-2.2.8
>> Starting 1 thread
>> rbd engine: RBD version: 0.1.9
>> Jobs: 1 (f=1): [W(1)] [100.0% done] [0KB/65405KB/0KB /s] [0/63/0 iops] [eta
>> 00m:00s]
>> job1: (groupid=0, jobs=1): err= 0: pid=43960: Fri Sep 11 12:54:25 2015
>> write: io=102400MB, bw=121882KB/s, iops=119, runt=860318msec
>> slat (usec): min=355, max=7300, avg=908.97, stdev=361.02
>> clat (msec): min=11, max=1468, avg=129.59, stdev=130.68
>> lat (msec): min=12, max=1468, avg=130.50, stdev=130.69
>> clat percentiles (msec):
>> | 1.00th=[ 21], 5.00th=[ 26], 10.00th=[ 29], 20.00th=[ 34],
>> | 30.00th=[ 37], 40.00th=[ 40], 50.00th=[ 44], 60.00th=[ 63],
>> | 70.00th=[ 233], 80.00th=[ 241], 90.00th=[ 269], 95.00th=[ 367],
>> | 99.00th=[ 553], 99.50th=[ 652], 99.90th=[ 832], 99.95th=[ 848],
>> | 99.99th=[ 1369]
>> bw (KB /s): min=20363, max=248543, per=100.00%, avg=124381.19,
>> stdev=42313.29
>> lat (msec) : 20=0.95%, 50=55.27%, 100=5.55%, 250=24.83%, 500=12.28%
>> lat (msec) : 750=0.89%, 1000=0.21%, 2000=0.01%
>> cpu : usr=9.58%, sys=1.15%, ctx=23883, majf=0, minf=2751023
>> IO depths : 1=1.2%, 2=3.0%, 4=9.7%, 8=68.3%, 16=17.8%, 32=0.0%,
>>> =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=92.5%, 8=4.3%, 16=3.2%, 32=0.0%, 64=0.0%,
>>> =64=0.0%
>> issued : total=r=0/w=102400/d=0, short=r=0/w=0/d=0,
>> drop=r=0/w=0/d=0
>> latency : target=0, window=0, percentile=100.00%, depth=16
>>
>> Run status group 0 (all jobs):
>> WRITE: io=102400MB, aggrb=121882KB/s, minb=121882KB/s,
>> maxb=121882KB/s, mint=860318msec, maxt=860318msec
>>
>> Disk stats (read/write):
>> dm-1: ios=0/2072, merge=0/0, ticks=0/233, in_queue=233, util=0.01%,
>> aggrios=1/2249, aggrmerge=7/559, aggrticks=9/254, aggrin_queue=261,
>> aggrutil=0.01%
>> sda: ios=1/2249, merge=7/559, ticks=9/254, in_queue=261, util=0.01%
>> [root@rcprsdc1r72-01-ac rafaell]#
>>
>> Cheers,
>> Raf
>>
>>
>> --
>> Rafael Lopez
>> Data Storage Administrator
>> Servers & Storage (eSolutions)
>>
>>
>> ________________________________________
>>
>> PLEASE NOTE: The information contained in this electronic mail message is
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>>
>>
>>
>>
>> --
>> Rafael Lopez
>> Data Storage Administrator
>> Servers & Storage (eSolutions)
>> +61 3 990 59118
>>
>>
>>
>>
>>
>> --
>> Rafael Lopez
>> Data Storage Administrator
>> Servers & Storage (eSolutions)
>> +61 3 990 59118
>
>
>
>
>
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