Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load.

["Glauber Costa" <glommer@gmail.com>]

On Wed, Nov 12, 2008 at 9:42 AM, Gleb Natapov <gleb@redhat.com> wrote:
> On Tue, Nov 11, 2008 at 02:17:49PM -0600, Anthony Liguori wrote:
>> Gleb Natapov wrote:
>>> On Mon, Nov 10, 2008 at 09:46:12AM -0600, Anthony Liguori wrote:
>>>   -usbdevice tablet has nothing to do with it. Qemu misses interrupt
>>> even
>>> without this option and with SDL screen it misses them in bunches when
>>> SDL redraws a screen. In case of vnc qemu misses interrupt because of
>>> fsync() call in raw_flush(), or so my instrumentation shows.
>>>
>>
>> Can you give this patch a spin?
>>
> Doesn't compile for me. fd_pool_inuse and fd_inuse are used but not
> defined.
>
>> This introduces a bdrv_aio_flush() which will wait for all existing AIO
>> operations to complete before indicating completion.  It also fixes up
>> IDE.  Fixing up SCSI will be a little more tricky but not much.  Since
>> we now use O_DSYNC, it's unnecessary to do an fsync (or an fdatasync).
>>
>> Assuming you're using IDE, this should eliminate any delays from fsync.
> I am using IDE.
>
>> SDL delays are unavoidable because it's going to come down to SDL doing
>> sychronous updates to the X server.  The proper long term solution here
>> would be to put SDL in it's own thread but I'm not too worried about
> And probably time-keeping deserves its own thread. And CPU execution
> too.

It might well be a stupid idea, (would have to benchmark it), but the
other day it occurred to me
that we could keep timekeeping in a separate _process_, with a shm
area, doing timekeeping
for all running guests.


-- 
Glauber  Costa.
"Free as in Freedom"
http://glommer.net

"The less confident you are, the more serious you have to act."