TestBot news

Jonas Maebe jonas-devlists at watlock.be
Mon Dec 5 13:00:27 CST 2016


On 05/12/16 01:33, Francois Gouget wrote:
> On Sun, 4 Dec 2016, Jonas Maebe wrote:
>
>> Francois Gouget wrote:
>>> Indeed during the revert vm1 shows no read traffic (lots of RAM to cache
>>> that), but a steady 6 MB/s stream of writes ! In contrast on vm2 writes
>>> quickly ramp up to 80 MB/s, then stop after ~5 seconds and QEMU just
>>> uses CPU for the last ~4 seconds.
>>
>> Maybe vm2 mounts its file systems with noatime?
>
> The VM hosts all use relatime which provides essentially all the
> benefits of noatime.

I actually meant the file system in the VM, but I guess there are 
Windows rather than Linux VMs? Additionally, what is the "revert" 
operation exactly? Is it like an "svn revert"/"git reset --hard HEAD" in 
the VM, or some qemu operation, or something else?

> But in this case I expect the writes all go to the qcow2 disk image and
> I know vm1 is capable of sustaining more than 6 MB/s writes (e.g. when
> copying >100 GB around).

One thing you could look at is the output of iostat on the host while 
the operations are going on, in partical the transactions-per-second, to 
check whether the issue is that one is using a lot of small writes (for 
what ever reason) while the other uses fewer, larger writes.


Jonas



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