Re: [PATCH 1/3] net/colo-compare.c: Create event_bh with the right AioContext

[Lukas Straub <lukasstraub2@web.de>]

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On Wed, 22 Apr 2020 09:03:00 +0000
"Zhang, Chen" <chen.zhang@intel.com> wrote:

> > -----Original Message-----
> > From: Lukas Straub <lukasstraub2@web.de>
> > Sent: Wednesday, April 22, 2020 4:43 PM
> > To: Zhang, Chen <chen.zhang@intel.com>
> > Cc: qemu-devel <qemu-devel@nongnu.org>; Li Zhijian
> > <lizhijian@cn.fujitsu.com>; Jason Wang <jasowang@redhat.com>; Marc-
> > André Lureau <marcandre.lureau@redhat.com>; Paolo Bonzini
> > <pbonzini@redhat.com>
> > Subject: Re: [PATCH 1/3] net/colo-compare.c: Create event_bh with the right
> > AioContext
> > 
> > On Wed, 22 Apr 2020 08:29:39 +0000
> > "Zhang, Chen" <chen.zhang@intel.com> wrote:
> >   
> > > > -----Original Message-----
> > > > From: Lukas Straub <lukasstraub2@web.de>
> > > > Sent: Thursday, April 9, 2020 2:34 AM
> > > > To: qemu-devel <qemu-devel@nongnu.org>
> > > > Cc: Zhang, Chen <chen.zhang@intel.com>; Li Zhijian
> > > > <lizhijian@cn.fujitsu.com>; Jason Wang <jasowang@redhat.com>; Marc-
> > > > André Lureau <marcandre.lureau@redhat.com>; Paolo Bonzini
> > > > <pbonzini@redhat.com>
> > > > Subject: [PATCH 1/3] net/colo-compare.c: Create event_bh with the
> > > > right AioContext
> > > >
> > > > qemu_bh_new will set the bh to be executed in the main loop. This
> > > > causes problems as colo_compare_handle_event assumes that it has
> > > > exclusive access the queues, which are also accessed in the
> > > > iothread. It also assumes that it runs in a different thread than
> > > > the caller and takes the appropriate locks.
> > > >
> > > > Create the bh with the AioContext of the iothread to fulfill these
> > > > assumptions.
> > > >  
> > >
> > > Looks good for me, I assume it will increase performance. Do you have  
> > related data?
> > 
> > No, this fixes several crashes because the queues where accessed
> > concurrently from multiple threads. Sorry for my bad wording.  
> 
> Can you describe some details about the crash? Step by step?
> Maybe I can re-produce and test it for this patch.

There is no clear test case. For me the crashes happened after 1-20h of runtime
with lots of checkpoints (800ms) and some network traffic. The coredump always
showed that two threads where doing operations on the queues simultaneously.
Unfortunately, I don't have the coredumps anymore.

Regards,
Lukas Straub

> Thanks
> Zhang Chen
> 
> > 
> > Regards,
> > Lukas Straub
> >   
> > > Thanks
> > > Zhang Chen
> > >  
> > > > Signed-off-by: Lukas Straub <lukasstraub2@web.de>
> > > > ---
> > > >  net/colo-compare.c | 3 ++-
> > > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/net/colo-compare.c b/net/colo-compare.c index
> > > > 10c0239f9d..1de4220fe2 100644
> > > > --- a/net/colo-compare.c
> > > > +++ b/net/colo-compare.c
> > > > @@ -890,6 +890,7 @@ static void colo_compare_handle_event(void
> > > > *opaque)
> > > >
> > > >  static void colo_compare_iothread(CompareState *s)  {
> > > > +    AioContext *ctx = iothread_get_aio_context(s->iothread);
> > > >      object_ref(OBJECT(s->iothread));
> > > >      s->worker_context = iothread_get_g_main_context(s->iothread);
> > > >
> > > > @@ -906,7 +907,7 @@ static void colo_compare_iothread(CompareState  
> > *s)  
> > > >      }
> > > >
> > > >      colo_compare_timer_init(s);
> > > > -    s->event_bh = qemu_bh_new(colo_compare_handle_event, s);
> > > > +    s->event_bh = aio_bh_new(ctx, colo_compare_handle_event, s);
> > > >  }
> > > >
> > > >  static char *compare_get_pri_indev(Object *obj, Error **errp)
> > > > --
> > > > 2.20.1  
> > >  
> 


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