linux-kernel - Re: [PATCH v2] dmaengine: xgene-dma: Disable memcpy operation due to performance drop

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Message-ID: <20151009161208.GJ3609@vkoul-mobl.iind.intel.com>
Date:	Fri, 9 Oct 2015 17:12:09 +0100
From:	Vinod Koul <vinod.koul@...el.com>
To:	Rameshwar Prasad Sahu <rsahu@....com>
Cc:	dan.j.williams@...el.com, dmaengine@...r.kernel.org, arnd@...db.de,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, jcm@...hat.com,
	patches@....com
Subject: Re: [PATCH v2] dmaengine: xgene-dma: Disable memcpy operation due to
 performance drop

On Thu, Oct 08, 2015 at 02:36:57PM +0530, Rameshwar Prasad Sahu wrote:
> The DMA engine supports memory copy, RAID5 XOR, RAID6 PQ, and other
> computations. But the bandwidth of the entire DMA engine is shared
> among all channels. This patch re-configures operations availability
> such that one can achieve maximum performance for XOR and PQ
> computation by removing the memory offload operations.
> 
> Signed-off-by: Rameshwar Prasad Sahu <rsahu@....com>
> ---
>  drivers/dma/xgene-dma.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/dma/xgene-dma.c b/drivers/dma/xgene-dma.c
> index 8d57b1b..cd38022 100644
> --- a/drivers/dma/xgene-dma.c
> +++ b/drivers/dma/xgene-dma.c
> @@ -1707,7 +1707,6 @@ static void xgene_dma_set_caps(struct xgene_dma_chan *chan,
>  	dma_cap_zero(dma_dev->cap_mask);
> 
>  	/* Set DMA device capability */
> -	dma_cap_set(DMA_MEMCPY, dma_dev->cap_mask);
>  	dma_cap_set(DMA_SG, dma_dev->cap_mask);

This will not work. Still clients can invoke memcpy operation. You need to
remove the callback

-- 
~Vinod
--
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