Re: [Xen-devel] [PATCH 1/3] qemu-xen-traditional: use O_DIRECT to open disk images for IDE

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 27 Mar 2012, Zhang, Yang Z wrote:
> > > > diff --git a/xenstore.c b/xenstore.c
> > > > index 4c483e2..ac90366 100644
> > > > --- a/xenstore.c
> > > > +++ b/xenstore.c
> > > > @@ -643,7 +643,7 @@ void xenstore_parse_domain_config(int hvm_domid)
> > > >             }
> > > >              pstrcpy(bs->filename, sizeof(bs->filename), params);
> > > >
> > > > -            flags = BDRV_O_CACHE_WB; /* snapshot and write-back */
> > > > +            flags = BDRV_O_NOCACHE;
> > > >              is_readonly = 0;
> > > >              if (pasprintf(&buf, "%s/mode", bpath) == -1)
> > > >                  continue;
> > > Any reason for this change?
> > 
> > performance and correctness: BDRV_O_NOCACHE in QEMU means opening the
> > disk image with O_DIRECT
> Doesn't cache mode have better performance than NOCACHE?

Actually you are correct. I think that this patch should be dropped from
the series. Of course we need O_DIRECT for QDISK otherwise we do loose
correctness but considering that IDE should only be used during
installation it can stay as it is.

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