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SubjectRe: [PATCH 0/6] RFC v2: mm: gup/dma tracking
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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.

> 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.

Did you re-run the baseline on the new unpatched base kernel and can
we see the before/after?

Tom.

> 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=741MiB/s (778MB/s), 741MiB/s-741MiB/s (778MB/s-778MB/s), io=1024MiB (1074MB), run=1381-1381msec
>
> Disk stats (read/write):
> nvme0n1: ios=216966/0, merge=0/0, ticks=6112/0, in_queue=704, util=91.34%

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