Re: [patch] block layer: kmemcheck fixes

[Arjan van de Ven]

Nick Piggin wrote:
> > > Maybe cpus these days have so much store bandwith that doing
> > > things like the above is OK, but I doubt it :-)
> > on modern x86 cpus the memset may even be faster if the memory isn't in 
> > cache;
> > the "explicit" method ends up doing Write Allocate on the cache lines
> > (so read them from memory) even though they then end up being written 
> > entirely.
> > With memset the CPU is told that the entire range is set to a new value, and
> > the WA can be avoided for the whole-cachelines in the range.
>
> Don't you have write combining store buffers? Or is it still speculatively
> issuing the reads even before the whole cacheline is combined?

x86 memory order model doesn't allow that quite; and you need a "series" of at least 64 bytes
without any other memory accesses in between even if it would....
not happening in practice.
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