From: William Lee Irwin III <wli@holomorphy.com>
To: Andrew Morton <akpm@osdl.org>
Cc: Marcelo Tosatti <marcelo.tosatti@cyclades.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] cacheline align pagevec structure
Date: Thu, 9 Sep 2004 16:09:05 -0700 [thread overview]
Message-ID: <20040909230905.GO3106@holomorphy.com> (raw)
In-Reply-To: <20040909155226.714dc704.akpm@osdl.org>
Marcelo Tosatti <marcelo.tosatti@cyclades.com> wrote:
>> I do not see a problem with changing pagevec to "15" page pointers either,
>> Andrew, is there a special reason for that "16"? Is intentional to align
>> to 64 kbytes (IO device alignment)? I dont think that matters much because
>> of the elevator which sorts and merges requests anyway?
On Thu, Sep 09, 2004 at 03:52:26PM -0700, Andrew Morton wrote:
> No, it was just a randomly-chosen batching factor.
> The tradeoff here is between
> a) lock acquisition frequency versus lock hold time (increasing the size
> helps).
> b) icache misses versus dcache misses. (increasing the size probably hurts).
> I suspect that some benefit would be seen from making the size very small
> (say, 4). And on some machines, making it larger might help.
Reducing arrival rates by an Omega(NR_CPUS) factor would probably help,
though that may blow the stack on e.g. larger Altixen. Perhaps
O(lg(NR_CPUS)), e.g. NR_CPUS > 1 ? 4*lg(NR_CPUS) : 4 etc., will suffice,
though we may have debates about how to evaluate lg(n) at compile-time...
Would be nice if calls to sufficiently simple __attribute__((pure))
functions with constant args were considered constant expressions by gcc.
-- wli
next prev parent reply other threads:[~2004-09-09 23:09 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-09-09 16:39 [PATCH] cacheline align pagevec structure Marcelo Tosatti
2004-09-09 22:49 ` Andrew Morton
2004-09-09 21:41 ` Marcelo Tosatti
2004-09-09 23:20 ` Andrew Morton
2004-09-09 22:52 ` Andrew Morton
2004-09-09 23:09 ` William Lee Irwin III [this message]
2004-09-09 22:12 ` Marcelo Tosatti
2004-09-09 23:59 ` William Lee Irwin III
2004-09-09 23:22 ` Andrew Morton
2004-09-10 0:07 ` [pagevec] resize pagevec to O(lg(NR_CPUS)) William Lee Irwin III
2004-09-10 4:56 ` Nick Piggin
2004-09-10 4:59 ` Nick Piggin
2004-09-10 17:49 ` Marcelo Tosatti
2004-09-12 0:29 ` Nick Piggin
2004-09-12 5:23 ` William Lee Irwin III
2004-09-12 4:36 ` Nick Piggin
2004-09-12 4:56 ` William Lee Irwin III
2004-09-12 4:28 ` Nick Piggin
2004-09-12 6:27 ` William Lee Irwin III
2004-09-12 6:03 ` Nick Piggin
2004-09-12 7:19 ` William Lee Irwin III
2004-09-12 7:42 ` Andrew Morton
2004-09-14 2:18 ` William Lee Irwin III
2004-09-14 2:57 ` Andrew Morton
2004-09-14 3:12 ` William Lee Irwin III
2004-09-12 8:57 ` William Lee Irwin III
2004-09-13 22:21 ` Marcelo Tosatti
2004-09-14 1:59 ` Nick Piggin
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