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

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Date:	Thu, 8 Oct 2015 14:27:07 +0530
From:	Rameshwar Sahu <rsahu@....com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Vinod Koul <vinod.koul@...el.com>, dan.j.williams@...el.com,
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	jcm@...hat.com, patches@....com
Subject: Re: [PATCH] dmaengine: xgene-dma: Disable memcpy operation due to
 performance drop

On Thu, Oct 8, 2015 at 2:23 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Thursday 08 October 2015 13:55:16 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 | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/dma/xgene-dma.c b/drivers/dma/xgene-dma.c
>> index 8d57b1b..2998fcb 100644
>> --- a/drivers/dma/xgene-dma.c
>> +++ b/drivers/dma/xgene-dma.c
>> @@ -154,6 +154,7 @@
>>  #define XGENE_DMA_MAX_XOR_SRC          5
>>  #define XGENE_DMA_16K_BUFFER_LEN_CODE  0x0
>>  #define XGENE_DMA_INVALID_LEN_CODE     0x7800000000000000ULL
>> +#undef XGENE_DMA_MEMCPY_ENABLE
>>
>>  /* X-Gene DMA descriptor error codes */
>>  #define ERR_DESC_AXI                   0x01
>> @@ -1707,7 +1708,9 @@ static void xgene_dma_set_caps(struct xgene_dma_chan *chan,
>>         dma_cap_zero(dma_dev->cap_mask);
>>
>>         /* Set DMA device capability */
>> +#ifdef XGENE_DMA_MEMCPY_ENABLE
>>         dma_cap_set(DMA_MEMCPY, dma_dev->cap_mask);
>> +#endif
>>         dma_cap_set(DMA_SG, dma_dev->cap_mask);
>>
>>         /* Basically here, the X-Gene SoC DMA engine channel 0 supports XOR
>
> I don't see what the #ifdef gains you here when the setting is
> hardcoded. Why not just remove that DMA_MEMCPY capability completely
> if you don't want to use it?

Okay Arnd,
>
>         Arnd
> --
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