Messages in this thread | | | Date | Fri, 26 Mar 2004 10:49:04 -0800 | From | Andrew Morton <> | Subject | Re: Fw: potential /dev/urandom scalability improvement |
| |
David Mosberger <davidm@napali.hpl.hp.com> wrote: > > >>>>> On Fri, 26 Mar 2004 11:06:19 +0000, Dave Jones <davej@redhat.com> 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! ;-)) >
But the start address which is fed into prefetch_range() may not be cacheline-aligned. So if appropriately abused, a prefetch_range() could wander off the end of the user's buffer and into a new page.
I think this gets it right, but I probably screwed something up.
static inline void prefetch_range(void *addr, size_t len) { #ifdef ARCH_HAS_PREFETCH char *cp; unsigned long end;
end = ((unsigned long)addr + len + PREFETCH_STRIDE - 1); end &= ~(PREFETCH_STRIDE - 1);
for (cp = addr; cp < (char *)end; cp += PREFETCH_STRIDE) prefetch(cp); #endif }
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |