linux-kernel - Re: [PATCH] virtio_ring: use smp_store

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Message-ID: <20151217143910.GD6344@twins.programming.kicks-ass.net>
Date:	Thu, 17 Dec 2015 15:39:10 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Jason Wang <jasowang@...hat.com>, qemu-devel@...gnu.org,
	Alexander Duyck <alexander.duyck@...il.com>
Subject: Re: [PATCH] virtio_ring: use smp_store_mb

On Thu, Dec 17, 2015 at 04:33:44PM +0200, Michael S. Tsirkin wrote:
> On Thu, Dec 17, 2015 at 02:57:26PM +0100, Peter Zijlstra wrote:
> > 
> > You could of course go fix that instead of mutilating things into
> > sort-of functional state.
> 
> Yes, we'd just need to touch all architectures, all for
> the sake of UP which almost no one uses.
> Basically, we need APIs that explicitly are
> for talking to another kernel on a different CPU on
> the same SMP system, and implemented identically
> between CONFIG_SMP and !CONFIG_SMP on all architectures.
> 
> Do you think this is something of general usefulness,
> outside virtio?

I'm not aware of any other case, but if there are more parts of virt
that need this then I see no problem adding it.

That is, virt in general is the only use-case that I can think of,
because this really is an artifact of interfacing with an SMP host while
running an UP kernel.

But I'm really not familiar with virt, so I do not know if there's more
sites outside of virtio that could use this.

Touching all archs is a tad tedious, but its fairly straight forward.
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