Re: Poor disk performance in NetBSD DomU, again

[Yi Qiao <qiaoy%qiaoy.info@localhost>]

On Mon, May 19, 2014 at 2:15 PM, Manuel Bouyer 
<bouyer%antioche.eu.org@localhost> wrote:
> Hello,
> the attached patch may help.
> What happens is that, even through the pagedaemon sends ordered
> write requests, dk_start() will probably dequeue and requeue them in a
> different order. This causes the underlying device to see out of order
> write requests and this seems to make a big difference for some devices.


Hi Manuel

  The patch works like a charm!! Thanks a ton for the effort.

  The following stats are gathered from a test pv based on 6.1.4
release install, with the patch applied to 6.1.4 release source and
XEN3_DOMU recompiled.

Write
=====
netbsd# dd if=/dev/zero of=testfile bs=32k count=131072
131072+0 records in
131072+0 records out
4294967296 bytes transferred in 37.852 secs (113467380 bytes/sec)

dom0$ iostat -d -x wd0 5
device  read KB/t    r/s   time     MB/s write KB/t    w/s   time     MB/s
wd0         16.00      2   0.97     0.03      53.48   1943   0.97   101.50
wd0         16.00      2   1.00     0.03      55.95   2135   1.00   116.67
wd0         16.00      3   0.99     0.04      54.86   1950   0.99   104.45

Read
====
netbsd# dd if=testfile of=/dev/null bs=32k
131072+0 records in
131072+0 records out
4294967296 bytes transferred in 36.141 secs (118839193 bytes/sec)

dom0$ iostat -d -x wd0 5
device  read KB/t    r/s   time     MB/s write KB/t    w/s   time     MB/s
wd0         61.83   1876   0.98   113.29      20.41      4   0.98     0.09
wd0         62.43   1915   1.00   116.72       4.80      1   1.00     0.00
wd0         62.42   1823   0.98   111.09       8.12      3   0.98     0.02

>
> --
> Manuel Bouyer <bouyer%antioche.eu.org@localhost>
>      NetBSD: 26 ans d'experience feront toujours la difference
> --