Re: [Xen-devel] [PATCH 05/10] xen: use SMP barrier in common code dealing with shared memory protocols

[Tim Deegan <tim@xxxxxxx>]

At 17:10 +0100 on 28 Jun (1372439451), Ian Campbell wrote:
> Xen currently makes no strong distinction between the SMP barriers (smp_mb
> etc) and the regular barrier (mb etc). In Linux, where we inherited these
> names from having imported Linux code which uses them, the SMP barriers are
> intended to be sufficient for implementing shared-memory protocols between
> processors in an SMP system while the standard barriers are useful for MMIO
> etc.
> 
> On x86 with the stronger ordering model there is not much practical difference
> here but ARM has weaker barriers available which are suitable for use as SMP
> barriers.
> 
> Therefore ensure that common code uses the SMP barriers when that is all which
> is required.
> 
> On both ARM and x86 both types of barrier are currently identical so there is
> no actual change. A future patch will change smp_mb to a weaker barrier on
> ARM.
> 
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

Reviewed-by: Tim Deegan <tim@xxxxxxx>


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