From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Pekka Enberg <penberg@kernel.org>
Cc: Sasha Levin <levinsasha928@gmail.com>,
kvm@vger.kernel.org, mingo@elte.hu, asias.hejun@gmail.com
Subject: Re: [PATCH] kvm tools: Support virtio indirect buffers
Date: Tue, 29 Nov 2011 17:06:10 +0400 [thread overview]
Message-ID: <20111129130610.GA1775@moon> (raw)
In-Reply-To: <alpine.LFD.2.02.1111291501360.9333@tux.localdomain>
On Tue, Nov 29, 2011 at 03:01:59PM +0200, Pekka Enberg wrote:
> >>
> >>Hi Sasha, where the rmb() then? Or maybe you wanted plain barrier() here?
> >
> >On the kernel side.
> >Theres a mb there which happens there during the kick.
>
> I guess we need to improve the comment in next_desc()?
>
Kernel's code has pretty good aliases for virtio barriers I think
#ifdef CONFIG_SMP
/* Where possible, use SMP barriers which are more lightweight than mandatory
* barriers, because mandatory barriers control MMIO effects on accesses
* through relaxed memory I/O windows (which virtio does not use). */
#define virtio_mb() smp_mb()
#define virtio_rmb() smp_rmb()
#define virtio_wmb() smp_wmb()
#else
/* We must force memory ordering even if guest is UP since host could be
* running on another CPU, but SMP barriers are defined to barrier() in that
* configuration. So fall back to mandatory barriers instead. */
#define virtio_mb() mb()
#define virtio_rmb() rmb()
#define virtio_wmb() wmb()
#endif
Maybe we could use somethig similar?
prev parent reply other threads:[~2011-11-29 13:06 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-28 17:54 [PATCH] kvm tools: Support virtio indirect buffers Sasha Levin
2011-11-28 18:49 ` Pekka Enberg
2011-11-28 20:17 ` Sasha Levin
2011-11-28 21:05 ` Sasha Levin
2011-11-30 5:20 ` Rusty Russell
2011-11-29 6:31 ` Cyrill Gorcunov
2011-11-29 7:45 ` Sasha Levin
2011-11-29 13:01 ` Pekka Enberg
2011-11-29 13:06 ` Cyrill Gorcunov [this message]
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