linux-kernel - Re: [PATCH 00/34] arch: barrier cleanup + __smp

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Date:	Wed, 30 Dec 2015 23:36:29 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	David Miller <davem@...emloft.net>
Cc:	linux-kernel@...r.kernel.org, peterz@...radead.org, arnd@...db.de,
	linux-arch@...r.kernel.org, andrew.cooper3@...rix.com,
	virtualization@...ts.linux-foundation.org,
	stefano.stabellini@...citrix.com
Subject: Re: [PATCH 00/34] arch: barrier cleanup + __smp_xxx barriers for virt

On Wed, Dec 30, 2015 at 03:46:46PM -0500, David Miller wrote:
> From: "Michael S. Tsirkin" <mst@...hat.com>
> Date: Wed, 30 Dec 2015 14:58:19 +0200
> 
> > -. Patch 1 documents the __smp APIs, and explains why they are
> >    useful for virt
> 
> If virt is doing things like interacting with descriptors that are
> shared with a (potentially SMP) host, why don't we just annotate those
> specific cases?

Using a bunch of per-arch ifdefs in virtio?
That's fundamentally what we have now.

But basically the rework reduces the LOC count in kernel anyway
by moving all ifdef CONFIG_SMP hacks into asm-generic.
So why not let virt benefit?

Or do you mean wrappers for __smp_XXX that explicitly
say they are for talking to host?
E.g. pv_mb() pv_rmb() etc.
That sounds very reasonable to me.

__smp_XXX things then become an implementation detail.

> The other memory barriers in the kernel do not matter for SMP'ness
> when build UP.
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