Re: guest suspend/resume & virtio: vring errors

[Gleb Natapov <gleb@redhat.com>]

On Sat, Jul 09, 2011 at 02:09:46PM +0400, Michael Tokarev wrote:
> 09.07.2011 13:55, Gleb Natapov wrote:
> > On Sat, Jul 09, 2011 at 01:47:25PM +0400, Michael Tokarev wrote:
> >> 09.07.2011 13:17, Gleb Natapov wrote:
> 
> >> This means that neither in-guest suspend/resume nor
> >> qemu-kvm migrate-to-file (which fails for a different
> >> reason I'm trying to debug now) works.  Which is very
> >> unfortunate.
> >>
> > Migration to file should work, or, at least, is a different problem.
> > It does not require guest cooperation.
> 
> Sure, that's why I said "different reason".  That's what
> prompted me to try in-guest migration - because I weren't
> able to use migrate-to-file, but I needed to replace the
> qemu-kvm binary after a security fix.
> 
> >> It does not work with any version of windows I tried, too
> >> (which is winXP, win7 32 and win7 64bits).  Windows enters
> >> an endless loop with a black screen during suspend (eating
> >> 100% CPU time).
> >>
> > Heh. Is this S4 or S3 suspend resume? Looks like recent breakage.
> > The only knows problem to me is in win7/2008 S3 resume + net.
> 
> How can I know if it's S3 or S4?  And I can't say it's recent:
S3 is suspend to memory, S4 is suspend to disk. Don't remember how
different version of Windows call them. Actually win7 disables S3
when running on qemu with cirrus adapter, so you are probably doing
S4.

> 0.14.1 works (or actually does not work) exactly the same in
> this respect as current git: suspend/resume is equally broken.
Suspend to disk worked flawlessly for me with Windows. There is nothing
special qemu should do for it to work. I haven't checked it on upstream
for a long time though. Can you check 0.12?

> 
> >> What's wrong/broken in linux?  Can it be fixed?
> >>
> > Complete lack of regression testing.
> 
> Hm.  You wrote:
> 
> > Yes, but Linux and suspend/resume are not best friends. Sometimes it
> > works by mistake, but next merged patch fixes it and suspend/resume
> > returns to its normal broken state.
> 
> So regression testing should detect and raise an alarm
> when it works by mistake.  But can it be fixed to work
> by design instead, after which regression testing gets
> entrirely new meaning ? :)
> 
Well S4/S3 is pet peeve of mine, so I little bit exaggerated :) Design
is not enough. Testing is needed. On Windows a driver that can't properly
handle S3/S4 will not pass WHQL, will not be signed by MS and will never
be loaded by the OS.

--
			Gleb.