Re: [Xen-users] Xen IO performance issues

[marki <list+xenusers@xxxxxxx>]

On 2018-09-20 11:49, marki wrote:
> Hello,
>
> On 2018-09-19 21:43, Hans van Kranenburg wrote:
> > Do things like using blk-mq make a difference here (just guessing 
> > around)?
> Honestly I'd have to find out first what that is. I'll check that out
> and will get back to you.

Even though something seems to exist, it doesn't look like it's active 
by default
# cat /sys/block/xvda/mq/0/active
0

There also does not seem to exist a parameter allowing to enable it:

# l /sys/module/xen_blkfront/parameters/
total 0
drwxr-xr-x 2 root root    0 Sep 20 13:28 ./
drwxr-xr-x 7 root root    0 Sep 20 13:28 ../
-r--r--r-- 1 root root 4096 Sep 20 13:28 max_indirect_segments
-r--r--r-- 1 root root 4096 Sep 20 13:28 max_ring_page_order

All other layers have it enabled alright:

# cat 
/sys/devices/pci0000:00/0000:00:01.1/ata1/host0/scsi_host/host0/use_blk_mq
1
# cat 
/sys/devices/pci0000:00/0000:00:01.1/ata2/host1/scsi_host/host1/use_blk_mq
1
# cat /sys/module/scsi_mod/parameters/use_blk_mq
Y
# cat /sys/module/dm_mod/parameters/use_blk_mq
Y

I have tried guessing and setting xen_blkfront.use_blk_mq=1 in the 
kernel parameters. No change.
# cat /sys/block/xvda/mq/0/active
0

I now also tried an Ubuntu 18 DomU (Kernel 4.15). Makes no differences. 
Except for iostat now showing the actual request size in kilobytes (44) 
and no longer in sectors (88).

BR,
Marki

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