Messages in this thread | | | Subject | Re: [PATCH 0/6] RFC v2: mm: gup/dma tracking | From | Tom Talpey <> | Date | Tue, 5 Feb 2019 08:38:10 -0500 |
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On 2/5/2019 3:22 AM, John Hubbard wrote: > On 2/4/19 5:41 PM, Tom Talpey wrote: >> On 2/4/2019 12:21 AM, john.hubbard@gmail.com wrote: >>> From: John Hubbard <jhubbard@nvidia.com> >>> >>> >>> Performance: here is an fio run on an NVMe drive, using this for the fio >>> configuration file: >>> >>> [reader] >>> direct=1 >>> ioengine=libaio >>> blocksize=4096 >>> size=1g >>> numjobs=1 >>> rw=read >>> iodepth=64 >>> >>> reader: (g=0): rw=read, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) >>> 4096B-4096B, ioengine=libaio, iodepth=64 >>> fio-3.3 >>> Starting 1 process >>> Jobs: 1 (f=1) >>> reader: (groupid=0, jobs=1): err= 0: pid=7011: Sun Feb 3 20:36:51 2019 >>> read: IOPS=190k, BW=741MiB/s (778MB/s)(1024MiB/1381msec) >>> slat (nsec): min=2716, max=57255, avg=4048.14, stdev=1084.10 >>> clat (usec): min=20, max=12485, avg=332.63, stdev=191.77 >>> lat (usec): min=22, max=12498, avg=336.72, stdev=192.07 >>> clat percentiles (usec): >>> | 1.00th=[ 322], 5.00th=[ 322], 10.00th=[ 322], 20.00th=[ >>> 326], >>> | 30.00th=[ 326], 40.00th=[ 326], 50.00th=[ 326], 60.00th=[ >>> 326], >>> | 70.00th=[ 326], 80.00th=[ 330], 90.00th=[ 330], 95.00th=[ >>> 330], >>> | 99.00th=[ 478], 99.50th=[ 717], 99.90th=[ 1074], 99.95th=[ >>> 1090], >>> | 99.99th=[12256] >> >> These latencies are concerning. The best results we saw at the end of >> November (previous approach) were MUCH flatter. These really start >> spiking at three 9's, and are sky-high at four 9's. The "stdev" values >> for clat and lat are about 10 times the previous. There's some kind >> of serious queuing contention here, that wasn't there in November. > > Hi Tom, > > I think this latency problem is also there in the baseline kernel, but... > >> >>> bw ( KiB/s): min=730152, max=776512, per=99.22%, avg=753332.00, >>> stdev=32781.47, samples=2 >>> iops : min=182538, max=194128, avg=188333.00, >>> stdev=8195.37, samples=2 >>> lat (usec) : 50=0.01%, 100=0.01%, 250=0.07%, 500=99.26%, 750=0.38% >>> lat (usec) : 1000=0.02% >>> lat (msec) : 2=0.24%, 20=0.02% >>> cpu : usr=15.07%, sys=84.13%, ctx=10, majf=0, minf=74 >> >> System CPU 84% is roughly double the November results of 45%. Ouch. > > That's my fault. First of all, I had a few extra, supposedly minor debug > settings in the .config, which I'm removing now--I'm doing a proper run > with the original .config file from November, below. Second, I'm not > sure I controlled the run carefully enough. > >> >> Did you re-run the baseline on the new unpatched base kernel and can >> we see the before/after? > > Doing that now, I see: > > -- No significant perf difference between before and after, but > -- Still high clat in the 99.99th > > ======================================================================= > Before: using commit 8834f5600cf3 ("Linux 5.0-rc5") > =================================================== > reader: (g=0): rw=read, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) > 4096B-4096B, ioengine=libaio, iodepth=64 > fio-3.3 > Starting 1 process > Jobs: 1 (f=1) > reader: (groupid=0, jobs=1): err= 0: pid=1829: Tue Feb 5 00:08:08 2019 > read: IOPS=193k, BW=753MiB/s (790MB/s)(1024MiB/1359msec) > slat (nsec): min=1269, max=40309, avg=1493.66, stdev=534.83 > clat (usec): min=127, max=12249, avg=329.83, stdev=184.92 > lat (usec): min=129, max=12256, avg=331.35, stdev=185.06 > clat percentiles (usec): > | 1.00th=[ 326], 5.00th=[ 326], 10.00th=[ 326], 20.00th=[ 326], > | 30.00th=[ 326], 40.00th=[ 326], 50.00th=[ 326], 60.00th=[ 326], > | 70.00th=[ 326], 80.00th=[ 326], 90.00th=[ 326], 95.00th=[ 326], > | 99.00th=[ 347], 99.50th=[ 519], 99.90th=[ 529], 99.95th=[ 537], > | 99.99th=[12125] > bw ( KiB/s): min=755032, max=781472, per=99.57%, avg=768252.00, > stdev=18695.90, samples=2 > iops : min=188758, max=195368, avg=192063.00, stdev=4673.98, > samples=2 > lat (usec) : 250=0.08%, 500=99.18%, 750=0.72% > lat (msec) : 20=0.02% > cpu : usr=12.30%, sys=46.83%, ctx=253554, majf=0, minf=74 > IO depths : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=0.1%, > >=64=100.0% > 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=0.1%, > >=64=0.0% > issued rwts: total=262144,0,0,0 short=0,0,0,0 dropped=0,0,0,0 > latency : target=0, window=0, percentile=100.00%, depth=64 > > Run status group 0 (all jobs): > READ: bw=753MiB/s (790MB/s), 753MiB/s-753MiB/s (790MB/s-790MB/s), > io=1024MiB (1074MB), run=1359-1359msec > > Disk stats (read/write): > nvme0n1: ios=221246/0, merge=0/0, ticks=71556/0, in_queue=704, > util=91.35% > > ======================================================================= > After: > ======================================================================= > reader: (g=0): rw=read, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) > 4096B-4096B, ioengine=libaio, iodepth=64 > fio-3.3 > Starting 1 process > Jobs: 1 (f=1) > reader: (groupid=0, jobs=1): err= 0: pid=1803: Mon Feb 4 23:58:07 2019 > read: IOPS=193k, BW=753MiB/s (790MB/s)(1024MiB/1359msec) > slat (nsec): min=1276, max=41900, avg=1505.36, stdev=565.26 > clat (usec): min=177, max=12186, avg=329.88, stdev=184.03 > lat (usec): min=178, max=12192, avg=331.42, stdev=184.16 > clat percentiles (usec): > | 1.00th=[ 326], 5.00th=[ 326], 10.00th=[ 326], 20.00th=[ 326], > | 30.00th=[ 326], 40.00th=[ 326], 50.00th=[ 326], 60.00th=[ 326], > | 70.00th=[ 326], 80.00th=[ 326], 90.00th=[ 326], 95.00th=[ 326], > | 99.00th=[ 359], 99.50th=[ 498], 99.90th=[ 537], 99.95th=[ 627], > | 99.99th=[12125] > bw ( KiB/s): min=754656, max=781504, per=99.55%, avg=768080.00, > stdev=18984.40, samples=2 > iops : min=188664, max=195378, avg=192021.00, stdev=4747.51, > samples=2 > lat (usec) : 250=0.12%, 500=99.40%, 750=0.46% > lat (msec) : 20=0.02% > cpu : usr=12.44%, sys=47.05%, ctx=252127, majf=0, minf=73 > IO depths : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=0.1%, > >=64=100.0% > 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=0.1%, > >=64=0.0% > issued rwts: total=262144,0,0,0 short=0,0,0,0 dropped=0,0,0,0 > latency : target=0, window=0, percentile=100.00%, depth=64 > > Run status group 0 (all jobs): > READ: bw=753MiB/s (790MB/s), 753MiB/s-753MiB/s (790MB/s-790MB/s), > io=1024MiB (1074MB), run=1359-1359msec > > Disk stats (read/write): > nvme0n1: ios=221203/0, merge=0/0, ticks=71291/0, in_queue=704, > util=91.19% > > How's this look to you?
Ok, I'm satisfied the four-9's latency spike is in not your code. :-) Results look good relative to baseline. Thanks for doublechecking!
Tom.
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