Re: [Xen-devel] Degregated I/O Performance since 3.4 - Regression in 3.4?

[Tobias Geiger <tobias.geiger@xxxxxxxxx>]

Am 23.04.2012 17:24, schrieb Konrad Rzeszutek Wilk:
> On Mon, Apr 23, 2012 at 12:53:03PM +0100, Stefano Stabellini wrote:
> > On Mon, 23 Apr 2012, Tobias Geiger wrote:
> > > Hello!
> > >
> > > i noticed a considerable drop in I/O Performance when using 3.4 (rc3 and rc4
> > > tested) as Dom0 Kernel;
> > >
> > > With 3.3 i get over 100mb/s in a HVM DomU (win64) with PV Drivers
> > > (gplpv_Vista2008x64_0.11.0.357.msi);
> > > With 3.4 it drops to about a third of that.
> > >
> > > Xen Version is xen-unstable:
> > > xen_changeset          : Tue Apr 17 19:13:52 2012 +0100 25209:e6b20ec1824c
> > >
> > > Disk config line is:
> > > disk = [ '/dev/vg_ssd/win7system,,hda' ]
> > > - it uses blkback.
> > I fail to see what could be the cause of the issue: nothing on the
> > blkback side should affect performances significantly.
> > You could try reverting the four patches to blkback that were applied
> > between 3.3 and 3.4-rc3 just to make sure it is not a blkback
> > regression:
> >
> > $ git shortlog v3.3..v3.4-rc3 drivers/block/xen-blkback
> > Daniel De Graaf (2):
> >        xen/blkback: use grant-table.c hypercall wrappers
> Hm.. Perhaps this patch fixes it a possible perf (I would think that
> the compiler would have kept the result of the first call to vaddr(req, i)
> somewhere.. but not sure) lost with the mentioned patch:
>
> diff --git a/drivers/block/xen-blkback/blkback.c 
> b/drivers/block/xen-blkback/blkback.c
> index 73f196c..65dbadc 100644
> --- a/drivers/block/xen-blkback/blkback.c
> +++ b/drivers/block/xen-blkback/blkback.c
> @@ -327,13 +327,15 @@ static void xen_blkbk_unmap(struct pending_req *req)
>         int ret;
>
>         for (i = 0; i<  req->nr_pages; i++) {
> +               unsigned long addr;
>                 handle = pending_handle(req, i);
>                 if (handle == BLKBACK_INVALID_HANDLE)
>                         continue;
> -               gnttab_set_unmap_op(&unmap[invcount], vaddr(req, i),
> +               addr = vaddr(req, i);
> +               gnttab_set_unmap_op(&unmap[invcount], addr,
>                                     GNTMAP_host_map, handle);
>                 pending_handle(req, i) = BLKBACK_INVALID_HANDLE;
> -               pages[invcount] = virt_to_page(vaddr(req, i));
> +               pages[invcount] = virt_to_page(addr);
>                 invcount++;
>         }
>
> >        xen/blkback: Enable blkback on HVM guests
> >
> > Konrad Rzeszutek Wilk (2):
> >        xen/blkback: Squash the discard support for 'file' and 'phy' type.
> >        xen/blkback: Make optional features be really optional.
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxx
> > http://lists.xen.org/xen-devel
that made it even worse :)
Write Performance is down to about 7mb/s (with 3.3: ~130mb/s)
Read "only" down to 40mb/s (with 3.3: ~140mb/s)

Greetings
Tobias

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