linux-kernel - Re: [PATCH 2/6]: powerpc/cell spidernet low watermark patch.

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Message-Id: <1156055509.5803.77.camel@localhost.localdomain>
Date:	Sun, 20 Aug 2006 16:31:49 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linuxppc-dev@...abs.org, akpm@...l.org,
	James K Lewis <jklewis@...ibm.com>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	Jeff Garzik <jgarzik@...ox.com>,
	ens Osterkamp <Jens.Osterkamp@...ibm.com>
Subject: Re: [PATCH 2/6]: powerpc/cell spidernet low watermark patch.


> card->low_watermark->next->dmac_cmd_status |= SPIDER_NET_DESCR_TXDESFLG;
> mb();
> card->low_watermark->dmac_cmd_status &= ~SPIDER_NET_DESCR_TXDESFLG;
> card->low_watermark = card->low_watermark->next;
> 
> when we queue another frame for TX.

I would have expected those to be racy vs. the hardware... what if the
hardware is updating dmac_cmd_status just as your are trying to and the
bit out of it ?

Ben


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