Re: [Qemu-devel] qemu disk use writeback don't take effect in centos 7.2 1511

[Paul Schlacter]

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 <address@hidden> 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 <address@hidden>
> 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 <
>> address@hidden> wrote:
>>
>>> * Paul Schlacter (address@hidden) 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 / address@hidden / Manchester, UK
>>>
>>
>>
>