Re: [Xen-devel] [PATCH] tools/libxc: make volatile keyword for bitmap operations optional

[Olaf Hering <olaf@xxxxxxxxx>]

On Mon, Jan 30, Keir Fraser wrote:

> On 30/01/2012 00:36, "Olaf Hering" <olaf@xxxxxxxxx> wrote:
> 
> > # HG changeset patch
> > # User Olaf Hering <olaf@xxxxxxxxx>
> > # Date 1327883694 -3600
> > # Node ID 5da4c273e819d5a1d42f3186f0829f8e00d83132
> > # Parent  b06617b0398c73c63ce153f39464fd1edac788e5
> > tools/libxc: make volatile keyword for bitmap operations optional
> > 
> > Except for xc_save, all bitmaps maintained by xc_bitops.h are used in single
> > threaded applications. So nothing will change the bitmaps content, adding
> > volatile adds just unneeded memory reloads.
> 
> The bitops aren't threadsafe anyway, as none of them use atomic rmw
> instructions. I suspect the volatile declarations are completely pointless
> and can just be removed.

Will gcc use the right thing if the array is passed to the hyperviso,
and will it reload everything after the hypercall? If yes, the volatile
can indeed go.

Olaf

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