linux-kernel - RE: [PATCH 20/29] ioat: switch watchdog and reset handler from workqueue to timer

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Date:	Mon, 14 Sep 2009 15:59:38 +0100
From:	"Sosnowski, Maciej" <maciej.sosnowski@...el.com>
To:	"Williams, Dan J" <dan.j.williams@...el.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH 20/29] ioat: switch watchdog and reset handler from
 workqueue	to timer

Williams, Dan J wrote:
> In order to support dynamic resizing of the descriptor ring or polling
> for a descriptor in the presence of a hung channel the reset handler
> needs to make progress while in a non-preemptible context.  The current
> workqueue implementation precludes polling channel reset completion
> under spin_lock().
> 
> This conversion also allows us to return to opportunistic cleanup in the
> ioat2 case as the timer implementation guarantees at least one cleanup
> after every descriptor is submitted.  This means the worst case
> completion latency becomes the timer frequency (for exceptional
> circumstances), but with the benefit of avoiding busy waiting when the
> lock is contended.
> 
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> ---

[...]
> --- a/drivers/dma/ioat/dma_v2.c
> +++ b/drivers/dma/ioat/dma_v2.c
> @@ -49,7 +49,7 @@ static void __ioat2_issue_pending(struct ioat2_dma_chan *ioat)
>  	void * __iomem reg_base = ioat->base.reg_base;
> 
>  	ioat->pending = 0;
> -	ioat->dmacount += ioat2_ring_pending(ioat);
> +	ioat->dmacount += ioat2_ring_pending(ioat);;
double semicolon

Signed-off-by: Maciej Sosnowski <maciej.sosnowski@...el.com>--
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