From: Paul Mackerras <paulus@samba.org>
To: "David S. Miller" <davem@davemloft.net>
Cc: olof@lixom.net, linux-kernel@vger.kernel.org,
linux-arch@vger.kernel.org, linuxppc-dev@ozlabs.org
Subject: Re: [RFC/PATCH] Make powerpc64 use __thread for per-cpu variables
Date: Wed, 10 May 2006 17:41:19 +1000 [thread overview]
Message-ID: <17505.39199.355967.509714@cargo.ozlabs.ibm.com> (raw)
In-Reply-To: <20060509.233958.73723993.davem@davemloft.net>
David S. Miller writes:
> That first cache line of current_thread_info() should be so hot that
> it's probably just fine to use current_thread_info()->task since
> you're just doing a mask on a fixed register (r1) to implement that.
I tried that, but I found that adding 1 instruction to the sequence
for getting current adds about 8k to the kernel text. Currently we do
it in one instruction, that would be two - the mask and the load. It
probably doesn't make a measurable difference to performance, but it
doesn't look good. The number of instructions we lose by using
__thread is much less than the 8k we gain from using
current_thread_info()->task for current. So I'd prefer to use a
per-cpu variable for current, since we can get to that in 1
instruction.
Paul.
next prev parent reply other threads:[~2006-05-10 7:41 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-05-10 4:03 [RFC/PATCH] Make powerpc64 use __thread for per-cpu variables Paul Mackerras
2006-05-10 5:16 ` Olof Johansson
2006-05-10 5:35 ` Alan Modra
2006-05-10 6:22 ` David S. Miller
2006-05-10 6:29 ` Paul Mackerras
2006-05-10 6:39 ` David S. Miller
2006-05-10 7:21 ` Benjamin Herrenschmidt
2006-05-10 7:41 ` Paul Mackerras [this message]
2006-05-10 10:14 ` David Howells
2006-05-10 15:47 ` Richard Henderson
2006-05-10 18:04 ` Steven Rostedt
2006-05-10 19:40 ` David S. Miller
2006-05-10 21:05 ` Paul Mackerras
2006-05-10 22:25 ` David S. Miller
2006-05-10 23:17 ` Segher Boessenkool
2006-05-11 0:22 ` Richard Henderson
2006-05-11 23:41 ` Segher Boessenkool
2006-05-11 1:04 ` Alan Modra
2006-05-11 1:21 ` Paul Mackerras
2006-05-11 2:01 ` Alan Modra
2006-05-11 23:42 ` Segher Boessenkool
2006-05-10 23:05 ` Paul Mackerras
2006-05-10 23:44 ` Paul Mackerras
2006-05-11 0:11 ` David S. Miller
2006-05-18 23:50 ` Paul Mackerras
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