From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Michael Cree <mcree@orcon.net.nz>
Cc: Ingo Molnar <mingo@elte.hu>,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-arch@vger.kernel.org, David Miller <davem@davemloft.net>,
Russell King <rmk@arm.linux.org.uk>
Subject: Re: Software prefetching considered harmful
Date: Sat, 21 May 2011 14:18:55 +1000 [thread overview]
Message-ID: <1305951535.7481.198.camel@pasglop> (raw)
In-Reply-To: <4DD73384.6080407@orcon.net.nz>
On Sat, 2011-05-21 at 15:37 +1200, Michael Cree wrote:
> While this is not a concern to the kernel (it obviously has access to
> location 0)
Not that obvious... dunno how you do your memory map on alpha but on
most architectures, 0 is userspace even when you're in the kernel and is
typically not mapped.
Cheers,
Ben.
> I can imagine some neophyte thinking (as I have done myself)
> "I'll look to see how the kernel implements lists and use that because
> it will be both clever and well tested code" without realising that the
> prefetch of a NULL is very inefficient for userspace!
>
>
next prev parent reply other threads:[~2011-05-21 4:19 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-19 17:12 Software prefetching considered harmful Linus Torvalds
2011-05-19 19:05 ` Linus Torvalds
2011-05-19 19:28 ` Ingo Molnar
2011-05-21 3:37 ` Michael Cree
2011-05-21 4:18 ` Benjamin Herrenschmidt [this message]
2011-05-21 10:42 ` Ingo Molnar
2011-05-19 19:32 ` David Miller
2011-05-19 19:38 ` Linus Torvalds
2011-05-19 19:47 ` David Miller
2011-05-19 23:34 ` Ingo Molnar
2011-05-20 16:01 ` Catalin Marinas
2011-05-20 1:42 ` Benjamin Herrenschmidt
2011-05-20 8:34 ` Ingo Molnar
2011-05-20 9:13 ` Benjamin Herrenschmidt
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