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Date: Wed, 16 Aug 2006 18:47:28 -0500
To: Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH 1/2]: powerpc/cell spidernet bottom half
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From: linas@austin.ibm.com (Linas Vepstas)
Cc: akpm@osdl.org, jeff@garzik.org, netdev@vger.kernel.org, jklewis@us.ibm.com,
	linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org,
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On Thu, Aug 17, 2006 at 01:03:20AM +0200, Arnd Bergmann wrote:
> 
> Could well be related to latencies when going to the remote
> node for descriptor DMAs. Have you tried if the hch's NUMA
> patch or using numactl makes a difference here?

No. I guess I should try.

> > > sounds like the right approach to simplify the code.
> >
> > Its not a big a driver. 'wc' says its 2.3 loc, which
> > is 1/3 or 1/5 the size of tg3.c or the e1000*c files.
> 
> Right, I was thinking of removing a lock or another, not
> throwing out half of the driver ;-)

There's only four lock points grand total. 
-- One on the receive side,
-- one to protect the transmit head pointer, 
-- one to protect the transmit tail pointer, 
-- one to protect the location of the transmit low watermark.

The last three share the same lock. I tried using distinct
locks, but this worsened things, probably due to cache-line 
trashing. I tried removing the head pointer lock, but this
failed. I don't know why, and was surprised by this. I thought
hard_start_xmit() was serialized.

--linas