Re: strange guest slowness after some time

[Tomasz Chmielewski <mangoo@wpkg.org>]

Rusty Russell schrieb:
> On Tuesday 07 April 2009 00:49:17 Tomasz Chmielewski wrote:
>> Tomasz Chmielewski schrieb:
>>
>>> As I mentioned, it was using virtio net.
>>>
>>> Guests running with e1000 (and virtio_blk) don't have this problem.
>> Also, virtio_console seem to be affected by this "slowness" issue.
> 
> I'm pretty sure this is different.  Older virtio_console code ignored
> interrupts and polled, and use a heuristic to back off on polling (this was
> because we used the generic "hvc" infrastructure which hacked support).

By "older" you mean guest drivers?
I have 2.6.27.x on guests and see this issue.
If you meant host, I use kvm-84.


> You'll find a delay on the first keystroke after idle, but none on the
> second.

I'm not sure.
Press "a" seven times fast, and 7 characters will be printed a second later.

But: wait one second more, it will be unresponsive again. You won't see 
the characters "as you type".


Also these symptoms are very similar to virtio_net issue:
- it happens only on some guest (even if they have the same kernel and 
userspace) after a random period of time
- it used to happen for me _always_ when network got slow with 
virtio_net driver
- it doesn't go away with guest restart initiated from guest's system
- it goes away with kvm process stop/start (i.e. new kvm process), but 
can appear later with no apparent cause



-- 
Tomasz Chmielewski
http://wpkg.org