Displaying 5 results from an estimated 5 matches for "fly6merba6mjeywwbbe7a5aaqsaknw".
2015 Dec 17
4
[PATCH] virtio_ring: use smp_store_mb
We need a full barrier after writing out event index, using smp_store_mb
there seems better than open-coding.
As usual, we need a wrapper to account for strong barriers/non smp.
It's tempting to use this in vhost as well, for that, we'll
need a variant of smp_store_mb that works on __user pointers.
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
Seems to give a speedup
2015 Dec 17
4
[PATCH] virtio_ring: use smp_store_mb
We need a full barrier after writing out event index, using smp_store_mb
there seems better than open-coding.
As usual, we need a wrapper to account for strong barriers/non smp.
It's tempting to use this in vhost as well, for that, we'll
need a variant of smp_store_mb that works on __user pointers.
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
Seems to give a speedup
2015 Dec 17
0
[PATCH] virtio_ring: use smp_store_mb
...E.g. as
> xchng faster than mfence on all/most intel CPUs? Anyone has an opinion?
Would help if you Cc people who would actually know this :-)
Yes, we've recently established that xchg is indeed faster than mfence
on at least recent machines, see:
lkml.kernel.org/r/CA+55aFynbkeuUGs9s-q+fLY6MeRBA6MjEyWWbbe7A5AaqsAknw at mail.gmail.com
> +static inline void virtio_store_mb(bool weak_barriers,
> + __virtio16 *p, __virtio16 v)
> +{
> +#ifdef CONFIG_SMP
> + if (weak_barriers)
> + smp_store_mb(*p, v);
> + else
> +#endif
> + {
> + WRITE_ONCE(*p, v);
> + mb();
> + }
> +...
2015 Dec 17
2
[PATCH] virtio_ring: use smp_store_mb
...opinion?
>
> Would help if you Cc people who would actually know this :-)
Good point. Glad you still saw this. Thanks!
> Yes, we've recently established that xchg is indeed faster than mfence
> on at least recent machines, see:
>
> lkml.kernel.org/r/CA+55aFynbkeuUGs9s-q+fLY6MeRBA6MjEyWWbbe7A5AaqsAknw at mail.gmail.com
>
> > +static inline void virtio_store_mb(bool weak_barriers,
> > + __virtio16 *p, __virtio16 v)
> > +{
> > +#ifdef CONFIG_SMP
> > + if (weak_barriers)
> > + smp_store_mb(*p, v);
> > + else
> > +#endif
> > + {
> &...
2015 Dec 17
2
[PATCH] virtio_ring: use smp_store_mb
...opinion?
>
> Would help if you Cc people who would actually know this :-)
Good point. Glad you still saw this. Thanks!
> Yes, we've recently established that xchg is indeed faster than mfence
> on at least recent machines, see:
>
> lkml.kernel.org/r/CA+55aFynbkeuUGs9s-q+fLY6MeRBA6MjEyWWbbe7A5AaqsAknw at mail.gmail.com
>
> > +static inline void virtio_store_mb(bool weak_barriers,
> > + __virtio16 *p, __virtio16 v)
> > +{
> > +#ifdef CONFIG_SMP
> > + if (weak_barriers)
> > + smp_store_mb(*p, v);
> > + else
> > +#endif
> > + {
> &...