Re: [Xen-devel] [PATCH v2 0/2] xen-block: fix sector size confusion

[Håkon Alstadheim <hakon@xxxxxxxxxxxxxxxxxx>]

Den 01.04.2019 11:34, skrev Kevin Wolf:
> Yes, for 512 accesses on native 4k disks with O_DIRECT, the QEMU block
> layer performs the necessary RMW. Of course, it still comes with a
> performance penalty, so you want to avoid such setups, but they do work.
I suspect that the approximately 1/10 -th disk-speed I see (e.g 28389 
vs  258719 K/sec sequential disk Output) in domU compared to dom0 must 
be due to this. I have dom0 and domU drives as partitions on an md 
raid6. The performance is sub-optimal to put it mildly. Here is one 
example bonnie++ run on a guest:
Version  1.97       ------Sequential Output------ --Sequential Input- 
--Random-
Concurrency   3     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- 
--Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  
/sec %CP
gt-credit2-on-p 16G  1062  90 28389   2 20233   2  3950  82 199633 10  
1195  17
Latency             19003us     140ms     652ms   20811us 602ms   33189us
Version  1.97       ------Sequential Create------ --------Random 
Create--------
gt-credit2-on-pt    -Create-- --Read--- -Delete-- -Create-- --Read--- 
-Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  
/sec %CP
                127 34445  26 +++++ +++ 42424  27 67418  51 +++++ +++ 
52590  35
Latency             12979us     329us    2903us     304us 38us     668us
1.97,1.97,gt-credit2-on-pt,3,1550928114,16G,,1062,90,28389,2,20233,2,3950,82,199633,10,1195,17,127,,,,,34445,26,+++++,+++,42424,27,67418,51,+++++,+++,52590,35,19003us,140ms,652ms,20811us,602ms,33189us,12979us,329us,2903us,304us,38us,668us


Same on dom0:

Version  1.97       ------Sequential Output------ --Sequential Input- 
--Random-
Concurrency   3     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- 
--Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  
/sec %CP
XEN-4.12-DOM0          16G   475  91 258719  20 151508  19   585 99 
324725  22 392.3  14
Latency             16093us    1097ms     406ms   18136us 160ms     155ms
Version  1.97       ------Sequential Create------ --------Random 
Create--------
XEN-4.12-DOM0              -Create-- --Read--- -Delete-- -Create-- 
--Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  
/sec %CP
                  8  6563  11 +++++ +++ 13522  20 10969  18 +++++ +++  
9560  13
Latency               104us      68us   18179us     120us 20us      63us
1.97,1.97,XEN-4.12-DOM0,3,1547961396,16G,,475,91,258719,20,151508,19,585,99,324725,22,392.3,14,8,,,,,6563,11,+++++,+++,13522,20,10969,18,+++++,+++,9560,13,16093us,1097ms,406ms,18136us,160ms,155ms,104us,68us,18179us,120us,20us,63us


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