linux-kernel - Re: [PATCH v4] dmaengine: qcom-bam: Process multiple pending descriptors

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Date:   Mon, 25 Sep 2017 11:50:55 +0530
From:   Vinod Koul <vinod.koul@...el.com>
To:     Sricharan R <sricharan@...eaurora.org>
Cc:     absahu@...eaurora.org, andy.gross@...aro.org,
        david.brown@...aro.org, dan.j.williams@...el.com,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        dmaengine-owner@...r.kernel.org, stanimir.varbanov@...aro.org,
        architt@...eaurora.org
Subject: Re: [PATCH v4] dmaengine: qcom-bam: Process multiple pending
 descriptors

On Mon, Aug 28, 2017 at 08:30:24PM +0530, Sricharan R wrote:
> The bam dmaengine has a circular FIFO to which we
> add hw descriptors that describes the transaction.
> The FIFO has space for about 4096 hw descriptors.
> 
> Currently we add one descriptor and wait for it to
> complete with interrupt and then add the next pending
> descriptor. In this way, the FIFO is underutilized
> since only one descriptor is processed at a time, although
> there is space in FIFO for the BAM to process more.
> 
> Instead keep adding descriptors to FIFO till its full,
> that allows BAM to continue to work on the next descriptor
> immediately after signalling completion interrupt for the
> previous descriptor.
> 
> Also when the client has not set the DMA_PREP_INTERRUPT for
> a descriptor, then do not configure BAM to trigger a interrupt
> upon completion of that descriptor. This way we get a interrupt
> only for the descriptor for which DMA_PREP_INTERRUPT was
> requested and there signal completion of all the previous completed
> descriptors. So we still do callbacks for all requested descriptors,
> but just that the number of interrupts are reduced.
> 
> CURRENT:
> 
>             ------      -------   ---------------
>             |DES 0|     |DESC 1|  |DESC 2 + INT |
>             ------      -------   ---------------
>                |           |            |
>                |           |            |
> INTERRUPT:   (INT)       (INT)	      (INT)
> CALLBACK:     (CB)        (CB)         (CB)
> 
> 		MTD_SPEEDTEST READ PAGE: 3560 KiB/s
> 		MTD_SPEEDTEST WRITE PAGE: 2664 KiB/s
> 		IOZONE READ: 2456 KB/s
> 		IOZONE WRITE: 1230 KB/s
> 
> 	bam dma interrupts (after tests): 96508
> 
> CHANGE:
> 
>         ------  -------    -------------
>         |DES 0| |DESC 1   |DESC 2 + INT |
>         ------  -------   --------------
> 				|
> 				|
>           		      (INT)
> 			      (CB for 0, 1, 2)
> 
> 		MTD_SPEEDTEST READ PAGE: 3860 KiB/s
> 		MTD_SPEEDTEST WRITE PAGE: 2837 KiB/s
> 		IOZONE READ: 2677 KB/s
> 		IOZONE WRITE: 1308 KB/s
> 
> 	bam dma interrupts (after tests): 58806

Applied, thanks.

Sorry for the delay, bad timing I guess :)

-- 
~Vinod