Date: Thu, 9 Sep 2004 19:12:38 -0300
From: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
To: William Lee Irwin III <wli@holomorphy.com>, Andrew Morton <akpm@osdl.org>,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] cacheline align pagevec structure
Message-ID: <20040909221238.GA6182@logos.cnet>
References: <20040909163929.GA4484@logos.cnet> <20040909155226.714dc704.akpm@osdl.org> <20040909230905.GO3106@holomorphy.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20040909230905.GO3106@holomorphy.com>
User-Agent: Mutt/1.5.5.1i
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1687
Lines: 30

On Thu, Sep 09, 2004 at 04:09:05PM -0700, William Lee Irwin III wrote:
> 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.

Let me see if I get you right - basically what you're suggesting is 
to depend PAGEVEC_SIZE on NR_CPUS?
-
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/