On Mon, Feb 22, 2010 at 05:08:00PM +0200, Avi Kivity wrote: > On 02/22/2010 04:57 PM, Michael S. Tsirkin wrote: >> >> >>>> There is no need (for this case). Older read cannot be reordered with >>>> write, writes are not reordered with other writes, writes by a single >>>> processor are observed in the same order by all processors. >>>> >>>> >>> Well, Linux does use sfence. >>> >> At least on 64 bit it doesnt. >> > > Right, I was looking at wmb(), not smp_wmb(). > >>> I imagine all arches need an instruction. For reads as well. >>> >>> Note, gcc has a __sync_synchronize() builtin that compiles to mfence on >>> x86. We might use that as a baseline for both rmb and wmb, and let each >>> arch override it incrementally. >>> >> This it what my patch did. Note it only works well for recent gcc. >> > > Do you know how recent? IIRC 4.3 has broken implementation. 4.4 seems OK as far as I can tell. > -- > error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
