Re: Fw: potential /dev/urandom scalability improvement

[David Mosberger]

>>>>> On Fri, 26 Mar 2004 11:06:19 +0000, Dave Jones <davej@xxxxxxxxxx> said:

  Dave> On Thu, Mar 25, 2004 at 06:00:14PM -0800, Andrew Morton wrote:
  >> +static inline void prefetch_range(void *addr, size_t len) +{
  >> +#ifdef ARCH_HAS_PREFETCH + char *cp; + char *end = addr + len; +
  >> + for (cp = addr; cp < end; cp += PREFETCH_STRIDE) +
  >> prefetch(cp); +#endif +} + #endif

  Dave> I think this may be dangerous on some CPUs, if may prefetch
  Dave> past the end of the buffer. Ie, if PREFETCH_STRIDE was 32, and
  Dave> len was 65, we'd end up prefetching 65->97. As well as being
  Dave> wasteful to cachelines, this can crash if theres for eg
  Dave> nothing mapped after the next page boundary.

Huh?  It only ever prefetches addresses that are _within_ the
specified buffer.  Of course it will prefetch entire cachelines, but I
hope you're not worried about cachlines crossing page-boundaries! ;-))

	--david
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