From: Andi Kleen <ak@muc.de>
To: Andrew Morton <akpm@osdl.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Fw: potential /dev/urandom scalability improvement
Date: Sat, 27 Mar 2004 02:29:12 +0100 [thread overview]
Message-ID: <m3fzbvqdqv.fsf@averell.firstfloor.org> (raw)
In-Reply-To: <1E4IT-7f3-21@gated-at.bofh.it> (Andrew Morton's message of "Fri, 26 Mar 2004 20:00:15 +0100")
Andrew Morton <akpm@osdl.org> writes:
>
> 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
> }
The memory/bus controller usually only has a limited queue of
outstanding transactions and for a big buffer you will likely overflow
it. Also usually on modern CPUs it is enough to do prefetch for 2-3
cache lines at the beginning, then an automatic hardware prefetcher
will kick in and take care of the rest.
-Andi
next parent reply other threads:[~2004-03-27 6:11 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1DLZM-8aK-67@gated-at.bofh.it>
[not found] ` <1DLZM-8aK-65@gated-at.bofh.it>
[not found] ` <1DOE1-20o-17@gated-at.bofh.it>
[not found] ` <1DOXn-2k7-5@gated-at.bofh.it>
[not found] ` <1DXxI-Z7-39@gated-at.bofh.it>
[not found] ` <1E467-6KK-17@gated-at.bofh.it>
[not found] ` <1E4IT-7f3-21@gated-at.bofh.it>
2004-03-27 1:29 ` Andi Kleen [this message]
2004-03-27 15:48 ` Fw: potential /dev/urandom scalability improvement Matt Mackall
[not found] <20040325141923.7080c6f0.akpm@osdl.org>
2004-03-25 22:47 ` Matt Mackall
2004-03-26 1:45 ` David Mosberger
2004-03-26 2:00 ` Andrew Morton
2004-03-26 2:10 ` David Mosberger
2004-03-26 4:07 ` Matt Mackall
2004-03-26 4:19 ` Matt Mackall
2004-03-26 4:51 ` David Mosberger
2004-03-26 5:15 ` Matt Mackall
2004-03-26 5:24 ` David Mosberger
2004-03-26 11:06 ` Dave Jones
2004-03-26 18:08 ` David Mosberger
2004-03-26 18:23 ` Dave Jones
2004-03-26 21:31 ` David Mosberger
2004-03-26 18:49 ` Andrew Morton
2004-03-26 20:25 ` David Mosberger
2004-03-26 20:33 ` Andrew Morton
2004-03-26 20:45 ` Arjan van de Ven
2004-03-26 21:17 ` Andrew Morton
2004-03-27 7:44 ` Arjan van de Ven
2004-03-26 21:12 ` David Mosberger
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