Messages in this thread Patch in this message | | | Date | Thu, 1 Dec 2011 10:12:37 +0200 | From | "Michael S. Tsirkin" <> | Subject | Re: [RFC] virtio: use mandatory barriers for remote processor vdevs |
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On Thu, Dec 01, 2011 at 12:58:59PM +1030, Rusty Russell wrote: > On Thu, 1 Dec 2011 01:13:07 +0200, "Michael S. Tsirkin" <mst@redhat.com> wrote: > > For x86, stores into memory are ordered. So I think that yes, smp_XXX > > can be selected at compile time. > > > > So let's forget the virtio strangeness for a minute, > > Hmm, we got away with light barriers because we knew we were not > *really* talking to a device. But now with virtio-mmio, turns out we > are :)
You think virtio-mmio this issue too? It's reported on remoteproc...
> I'm really tempted to revert d57ed95 for 3.2, and we can revisit this > optimization later if it proves worthwhile. > > Thoughts? > Rusty.
Generally it does seem the best we can do for 3.2.
Given it's rc3, I'd be a bit wary of introducing regressions - I'll try to find some real setups (as in - not my laptop) to run some benchmarks on, to verify there's no major problem. I hope I can report on this in about a week from now - want to hold onto this meanwhile?
Further, if we do revert, need to remember to apply the following beforehand, to avoid breaking virtio tool:
tools/virtio: implement mandatory barriers for x86
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
diff --git a/tools/virtio/linux/virtio.h b/tools/virtio/linux/virtio.h index 68b8b8d..1bf0e80 100644 --- a/tools/virtio/linux/virtio.h +++ b/tools/virtio/linux/virtio.h @@ -172,11 +172,18 @@ struct virtqueue { #define MODULE_LICENSE(__MODULE_LICENSE_value) \ const char *__MODULE_LICENSE_name = __MODULE_LICENSE_value #define CONFIG_SMP #if defined(__i386__) || defined(__x86_64__) #define barrier() asm volatile("" ::: "memory") #define mb() __sync_synchronize() +#if defined(__i386__) +#define wmb() mb() +#define rmb() mb() +#else +#define wmb() asm volatile("sfence" ::: "memory") +#define rmb() asm volatile("lfence" ::: "memory") +#endif #define smp_mb() mb() # define smp_rmb() barrier() -- MST
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