[pve-devel] Fwd: Re: [Qemu-devel] [PATCH] rbd : disable rbd_cache_writethrough_until_flush for cache=unsafe

Fabian Gr├╝nbichler f.gruenbichler at proxmox.com
Thu Sep 22 08:49:42 CEST 2016


On Thu, Sep 22, 2016 at 08:30:18AM +0200, Stefan Priebe - Profihost AG wrote:
> 
> Is that one already in PVE?
> 

yes, since pve-qemu-kvm 2.6.1-1

https://git.proxmox.com/?p=pve-qemu-kvm.git;a=commit;h=6e9e99dd1de7f0ea0376c9c16bb49d2cbffe1267

> -------- Weitergeleitete Nachricht --------
> Betreff: Re: [Qemu-devel] [PATCH] rbd : disable
> rbd_cache_writethrough_until_flush for cache=unsafe
> Datum: Wed, 21 Sep 2016 18:01:44 -0700
> Von: Josh Durgin <jdurgin at redhat.com>
> An: Alexandre Derumier <aderumier at odiso.com>, qemu-devel at nongnu.org
> Kopie (CC): ceph-devel at vger.kernel.org
> 
> On 07/27/2016 05:26 AM, Alexandre Derumier wrote:
> > ceph force writethrough until a flush is detected.
> > With cache=unsafe, we never send flush.
> > So we need to tell to ceph
> > to set rbd_cache_writethrough_until_flush=false in this case.
> >
> > This speedup a lot qemu-img convert which use cache=unsafe by default
> >
> > Signed-off-by: Alexandre Derumier <aderumier at odiso.com>
> 
> Sorry for the delay - this is correct and needed since this option
> appeared by default in Ceph hammer.
> 
> Reviewed-by: Josh Durgin <jdurgin at redhat.com>
> 
> > ---
> >  block/rbd.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/block/rbd.c b/block/rbd.c
> > index 0106fea..f3af6c8 100644
> > --- a/block/rbd.c
> > +++ b/block/rbd.c
> > @@ -552,6 +552,10 @@ static int qemu_rbd_open(BlockDriverState *bs, QDict *options, int flags,
> >          rados_conf_set(s->cluster, "rbd_cache", "true");
> >      }
> >
> > +    if (flags & BDRV_O_NO_FLUSH) {
> > +        rados_conf_set(s->cluster, "rbd_cache_writethrough_until_flush", "false");
> > +    }
> > +
> >      r = rados_connect(s->cluster);
> >      if (r < 0) {
> >          error_setg_errno(errp, -r, "error connecting");
> >
> 
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