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The dax window I set is not very large (for example, 512MB). I am worried that the setting is too large. After a lot of VM workloads are started, it will take up a lot of memory (I know it is a mapping technology). If this setting is large, will it be a problem? , Such as 10G, 50G?
The following is my test performance data, it seems that the results are quite different, I don’t know why?

fio --name=small-file-multi-read --directory=/usr/share/nginx/html \
    --rw=randread --file_service_type=sequential \
    --bs=4k --filesize=10M --nrfiles=100 \
    --runtime=60 --time_based --numjobs=1 
 ...   
small-file-multi-read: (groupid=0, jobs=1): err= 0: pid=190: Mon Jul  5 07:05:18 2021
  read: IOPS=12.0k, BW=46.0MiB/s (49.2MB/s)(212MiB/4505msec)

fio --name=5G-bigfile-rand-read     --directory=/usr/share/nginx/html     --rw=randread --size=5G --bs=4k     --runtime=60 --time_based     --numjobs=1 
...
5G-bigfile-rand-read: (groupid=0, jobs=1): err= 0: pid=184: Mon Jul  5 06:57:08 2021
  read: IOPS=1255, BW=5024KiB/s (5144kB/s)(294MiB/60002msec)



在 2021/7/7 下午8:44，“Vivek Goyal”<vgoyal at redhat.com> 写入:

    On Fri, Jul 02, 2021 at 10:57:43AM +0200, Fabiano Fidêncio wrote:
    > Ryo Li,
    > 
    > On Thu, Jul 1, 2021 at 11:49 AM 李瑞友 <liruiyou at huayun.com> wrote:
    > >
    > > Hi guys
    > >
    > > I want to build a test scenario to see the difference in performance between the size of DAX windows and the size of read files. But it's not that I don't know how to build.
    > >
    > > I tried the following two methods, but it seems that the performance results are similar
    
    I am not sure what's the expectation. Why changing file size should change
    the throughput significantly. If DAX window is big enough to accomodate
    both small file and large file completely, then I/O rate will probably
    be same/similar.
    
    Thanks
    Vivek
    
    > >
    > >
    > >
    > > fio -filename=/usr/share/nginx/html/400MBfile --rw=randread --loops=10 --group_reporting --name=400MBfile
    > >
    > >
    > >
    > > fio -filename=/usr/share/nginx/html/5Gfile --rw=randread -bs=16k --group_reporting --name=5Gfile
    > >
    > >
    > >
    > > sh-4.4# fio -filename=/usr/share/nginx/html/5Gfile  --rw=randread -bs=16k  --group_reporting --name=5Gfile
    > >
    > > 5Gfile: (g=0): rw=randread, bs=(R) 16.0KiB-16.0KiB, (W) 16.0KiB-16.0KiB, (T) 16.0KiB-16.0KiB, ioengine=psync, iodepth=1
    > >
    > > fio-3.19
    > >
    > > Starting 1 process
    > >
    > > Jobs: 1 (f=1): [r(1)][100.0%][r=148MiB/s][r=9450 IOPS][eta 00m:00s]
    > >
    > > 5Gfile: (groupid=0, jobs=1): err= 0: pid=139: Thu Jul  1 09:38:07 2021
    > >
    > >   read: IOPS=9931, BW=155MiB/s (163MB/s)(5120MiB/32993msec)
    > >
    > >     clat (usec): min=52, max=18734, avg=95.79, stdev=69.49
    > >
    > >      lat (usec): min=53, max=18735, avg=96.47, stdev=69.53
    > >
    > >     clat percentiles (usec):
    > >
    > >      |  1.00th=[   61],  5.00th=[   64], 10.00th=[   66], 20.00th=[   71],
    > >
    > >      | 30.00th=[   75], 40.00th=[   79], 50.00th=[   82], 60.00th=[   88],
    > >
    > >      | 70.00th=[   97], 80.00th=[  114], 90.00th=[  141], 95.00th=[  163],
    > >
    > >      | 99.00th=[  235], 99.50th=[  293], 99.90th=[  734], 99.95th=[  807],
    > >
    > >      | 99.99th=[ 1287]
    > >
    > >    bw (  KiB/s): min=87471, max=191168, per=100.00%, avg=159511.97, stdev=18299.18, samples=65
    > >
    > >    iops        : min= 5466, max=11948, avg=9969.48, stdev=1143.77, samples=65
    > >
    > >   lat (usec)   : 100=72.93%, 250=26.28%, 500=0.52%, 750=0.19%, 1000=0.06%
    > >
    > >   lat (msec)   : 2=0.01%, 4=0.01%, 10=0.01%, 20=0.01%
    > >
    > >   cpu          : usr=6.04%, sys=46.45%, ctx=329379, majf=1, minf=13
    > >
    > >   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 rwts: total=327680,0,0,0 short=0,0,0,0 dropped=0,0,0,0
    > >
    > >      latency   : target=0, window=0, percentile=100.00%, depth=1
    > >
    > >
    > >
    > > Run status group 0 (all jobs):
    > >
    > >    READ: bw=155MiB/s (163MB/s), 155MiB/s-155MiB/s (163MB/s-163MB/s), io=5120MiB (5369MB), run=32993-32993msec
    > 
    > 
    > I've looped in some folks from Red Hat and Intel who have been working
    > with virtiofs, either on performance, on integration, or on virtiofs
    > itself.
    > I think they'll be able to provide you with some valuable feedback.
    > 
    > Please, mind that due to July 4th I think folks from the US may be off
    > for the next few days.
    > 
    > Best Regards,
    > -- 
    > Fabiano Fidêncio
    >