* [Qemu-devel] qemu disk use writeback don't take effect in centos 7.2 1511
@ 2017-11-01 7:44 Paul Schlacter
2017-11-01 9:45 ` Dr. David Alan Gilbert
0 siblings, 1 reply; 6+ messages in thread
From: Paul Schlacter @ 2017-11-01 7:44 UTC (permalink / raw)
To: qemu-devel
qemu version: 2.9.0
image: centos 7.2 1511 raw
cache mode: writeback
In centos7.2 time, the use of writeback and none, the result of dd disk is
the same io, no change
But I replaced centos7.1 centos7.3 centos7.4 when writeback was
significantly faster than none
Would like to ask what is going on, how to solve ?
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Qemu-devel] qemu disk use writeback don't take effect in centos 7.2 1511
2017-11-01 7:44 [Qemu-devel] qemu disk use writeback don't take effect in centos 7.2 1511 Paul Schlacter
@ 2017-11-01 9:45 ` Dr. David Alan Gilbert
[not found] ` <CADak6y485_OSHrzji4Wq7_3vOrK+ch6Vm1FW1RMidSzoO3U-kQ@mail.gmail.com>
0 siblings, 1 reply; 6+ messages in thread
From: Dr. David Alan Gilbert @ 2017-11-01 9:45 UTC (permalink / raw)
To: Paul Schlacter; +Cc: qemu-devel
* Paul Schlacter (wlfightup@gmail.com) wrote:
> qemu version: 2.9.0
> image: centos 7.2 1511 raw
> cache mode: writeback
>
>
> In centos7.2 time, the use of writeback and none, the result of dd disk is
> the same io, no change
>
> But I replaced centos7.1 centos7.3 centos7.4 when writeback was
> significantly faster than none
>
> Would like to ask what is going on, how to solve ?
Hi Paul,
Can you just clarify your setup please; do you mean that
with the same qemu setup but a 7.2 guest rather than a 7.1/7.3 guest
the behaviour changes?
Dave
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Qemu-devel] qemu disk use writeback don't take effect in centos 7.2 1511
[not found] ` <CADak6y485_OSHrzji4Wq7_3vOrK+ch6Vm1FW1RMidSzoO3U-kQ@mail.gmail.com>
@ 2017-11-01 12:03 ` Paul Schlacter
2017-11-03 3:46 ` Paul Schlacter
0 siblings, 1 reply; 6+ messages in thread
From: Paul Schlacter @ 2017-11-01 12:03 UTC (permalink / raw)
To: Dr. David Alan Gilbert, qemu-devel
Hi David:
yes, with the same qemu, centos 7.2 guest cache is writeback and
none, the disk io almost, writeback feeling no effect.
but 7.1/7.3/7.4 cache is writeback was significantly faster than
none model
On Wed, Nov 1, 2017 at 8:02 PM, Paul Schlacter <wlfightup@gmail.com> wrote:
> Hi David:
> yes, with the same qemu, centos 7.2 guest cache is writeback and
> none, the disk io almost, writeback feeling no effect.
> but 7.1/7.3/7.4 cache is writeback was significantly faster than
> none model
>
> On Wed, Nov 1, 2017 at 5:45 PM, Dr. David Alan Gilbert <
> dgilbert@redhat.com> wrote:
>
>> * Paul Schlacter (wlfightup@gmail.com) wrote:
>> > qemu version: 2.9.0
>> > image: centos 7.2 1511 raw
>> > cache mode: writeback
>> >
>> >
>> > In centos7.2 time, the use of writeback and none, the result of dd disk
>> is
>> > the same io, no change
>> >
>> > But I replaced centos7.1 centos7.3 centos7.4 when writeback was
>> > significantly faster than none
>> >
>> > Would like to ask what is going on, how to solve ?
>>
>> Hi Paul,
>> Can you just clarify your setup please; do you mean that
>> with the same qemu setup but a 7.2 guest rather than a 7.1/7.3 guest
>> the behaviour changes?
>>
>> Dave
>>
>> --
>> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>>
>
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Qemu-devel] qemu disk use writeback don't take effect in centos 7.2 1511
2017-11-01 12:03 ` Paul Schlacter
@ 2017-11-03 3:46 ` Paul Schlacter
2017-11-03 9:10 ` Dr. David Alan Gilbert
0 siblings, 1 reply; 6+ messages in thread
From: Paul Schlacter @ 2017-11-03 3:46 UTC (permalink / raw)
To: Dr. David Alan Gilbert; +Cc: qemu-devel
latest progress：
use centos 7.2 https://cloud.centos.org/centos/7/images/
test version: 1511 1601 1604 1606 1608
>From the above version in turn test, found the previous version 1511 1601
1603 have the problem,
The latter two versions 1606 1608 are normal, dont't have the prblem,
Normal is cache = writeback io significantly higher than none mode
why?
On Wed, Nov 1, 2017 at 8:03 PM, Paul Schlacter <wlfightup@gmail.com> wrote:
> Hi David:
> yes, with the same qemu, centos 7.2 guest cache is writeback and
> none, the disk io almost, writeback feeling no effect.
> but 7.1/7.3/7.4 cache is writeback was significantly faster than
> none model
>
> On Wed, Nov 1, 2017 at 8:02 PM, Paul Schlacter <wlfightup@gmail.com>
> wrote:
>
>> Hi David:
>> yes, with the same qemu, centos 7.2 guest cache is writeback and
>> none, the disk io almost, writeback feeling no effect.
>> but 7.1/7.3/7.4 cache is writeback was significantly faster than
>> none model
>>
>> On Wed, Nov 1, 2017 at 5:45 PM, Dr. David Alan Gilbert <
>> dgilbert@redhat.com> wrote:
>>
>>> * Paul Schlacter (wlfightup@gmail.com) wrote:
>>> > qemu version: 2.9.0
>>> > image: centos 7.2 1511 raw
>>> > cache mode: writeback
>>> >
>>> >
>>> > In centos7.2 time, the use of writeback and none, the result of dd
>>> disk is
>>> > the same io, no change
>>> >
>>> > But I replaced centos7.1 centos7.3 centos7.4 when writeback was
>>> > significantly faster than none
>>> >
>>> > Would like to ask what is going on, how to solve ?
>>>
>>> Hi Paul,
>>> Can you just clarify your setup please; do you mean that
>>> with the same qemu setup but a 7.2 guest rather than a 7.1/7.3 guest
>>> the behaviour changes?
>>>
>>> Dave
>>>
>>> --
>>> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>>>
>>
>>
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Qemu-devel] qemu disk use writeback don't take effect in centos 7.2 1511
2017-11-03 3:46 ` Paul Schlacter
@ 2017-11-03 9:10 ` Dr. David Alan Gilbert
2017-11-03 10:09 ` Stefan Hajnoczi
0 siblings, 1 reply; 6+ messages in thread
From: Dr. David Alan Gilbert @ 2017-11-03 9:10 UTC (permalink / raw)
To: Paul Schlacter, stefanha; +Cc: qemu-devel
* Paul Schlacter (wlfightup@gmail.com) wrote:
> latest progress：
> use centos 7.2 https://cloud.centos.org/centos/7/images/
> test version: 1511 1601 1604 1606 1608
>
> From the above version in turn test, found the previous version 1511 1601
> 1603 have the problem,
> The latter two versions 1606 1608 are normal, dont't have the prblem,
> Normal is cache = writeback io significantly higher than none mode
>
> why?
It's a fun bug, but I don't know the cause - the fact it's dependent
on guest version but fixed, suggests something changed in the guest
kernel. If you really wanted to figure out why I guess the only way
would be to walk through the CentOS guest kernel versions and find the
exact kernel that fixed it; then we could hunt down which change fixed
it.
(I've cc'd in Stefan for block stuff, but this is sounding more guest
than qemu)
Dave
> On Wed, Nov 1, 2017 at 8:03 PM, Paul Schlacter <wlfightup@gmail.com> wrote:
>
> > Hi David:
> > yes, with the same qemu, centos 7.2 guest cache is writeback and
> > none, the disk io almost, writeback feeling no effect.
> > but 7.1/7.3/7.4 cache is writeback was significantly faster than
> > none model
> >
> > On Wed, Nov 1, 2017 at 8:02 PM, Paul Schlacter <wlfightup@gmail.com>
> > wrote:
> >
> >> Hi David:
> >> yes, with the same qemu, centos 7.2 guest cache is writeback and
> >> none, the disk io almost, writeback feeling no effect.
> >> but 7.1/7.3/7.4 cache is writeback was significantly faster than
> >> none model
> >>
> >> On Wed, Nov 1, 2017 at 5:45 PM, Dr. David Alan Gilbert <
> >> dgilbert@redhat.com> wrote:
> >>
> >>> * Paul Schlacter (wlfightup@gmail.com) wrote:
> >>> > qemu version: 2.9.0
> >>> > image: centos 7.2 1511 raw
> >>> > cache mode: writeback
> >>> >
> >>> >
> >>> > In centos7.2 time, the use of writeback and none, the result of dd
> >>> disk is
> >>> > the same io, no change
> >>> >
> >>> > But I replaced centos7.1 centos7.3 centos7.4 when writeback was
> >>> > significantly faster than none
> >>> >
> >>> > Would like to ask what is going on, how to solve ?
> >>>
> >>> Hi Paul,
> >>> Can you just clarify your setup please; do you mean that
> >>> with the same qemu setup but a 7.2 guest rather than a 7.1/7.3 guest
> >>> the behaviour changes?
> >>>
> >>> Dave
> >>>
> >>> --
> >>> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> >>>
> >>
> >>
> >
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Qemu-devel] qemu disk use writeback don't take effect in centos 7.2 1511
2017-11-03 9:10 ` Dr. David Alan Gilbert
@ 2017-11-03 10:09 ` Stefan Hajnoczi
0 siblings, 0 replies; 6+ messages in thread
From: Stefan Hajnoczi @ 2017-11-03 10:09 UTC (permalink / raw)
To: Paul Schlacter; +Cc: stefanha, qemu-devel, Dr. David Alan Gilbert
[-- Attachment #1: Type: text/plain, Size: 1201 bytes --]
On Fri, Nov 03, 2017 at 09:10:45AM +0000, Dr. David Alan Gilbert wrote:
> * Paul Schlacter (wlfightup@gmail.com) wrote:
> > latest progress：
> > use centos 7.2 https://cloud.centos.org/centos/7/images/
> > test version: 1511 1601 1604 1606 1608
> >
> > From the above version in turn test, found the previous version 1511 1601
> > 1603 have the problem,
> > The latter two versions 1606 1608 are normal, dont't have the prblem,
> > Normal is cache = writeback io significantly higher than none mode
> >
> > why?
>
> It's a fun bug, but I don't know the cause - the fact it's dependent
> on guest version but fixed, suggests something changed in the guest
> kernel. If you really wanted to figure out why I guess the only way
> would be to walk through the CentOS guest kernel versions and find the
> exact kernel that fixed it; then we could hunt down which change fixed
> it.
>
> (I've cc'd in Stefan for block stuff, but this is sounding more guest
> than qemu)
Please provide full details of the problem you are observing:
1. qemu command-line on the host (ps aux | grep qemu)
2. dd command-line inside the guest
3. "Good" output and "bad" output
Stefan
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^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2017-11-03 10:09 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2017-11-01 7:44 [Qemu-devel] qemu disk use writeback don't take effect in centos 7.2 1511 Paul Schlacter
2017-11-01 9:45 ` Dr. David Alan Gilbert
[not found] ` <CADak6y485_OSHrzji4Wq7_3vOrK+ch6Vm1FW1RMidSzoO3U-kQ@mail.gmail.com>
2017-11-01 12:03 ` Paul Schlacter
2017-11-03 3:46 ` Paul Schlacter
2017-11-03 9:10 ` Dr. David Alan Gilbert
2017-11-03 10:09 ` Stefan Hajnoczi
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