On Wed, Jul 20, 2016 at 11:50:32AM +0300, Peter Ujfalusi wrote:
> sDMA in OMAP3630 or newer SoC have support for LinkedList transfer. When
> LinkedList or Descriptor load feature is present we can create the
> descriptors for each and program sDMA to walk through the list of
> descriptors instead of the current way of sDMA stop, sDMA reconfiguration
> and sDMA start after each SG transfer.
> By using LinkedList transfer in sDMA the number of DMA interrupts will
> decrease dramatically.
> Booting up the board with filesystem on SD card for example:
> W/o LinkedList support:
> 27: 4436 0 WUGEN 13 Level omap-dma-engine
>
> Same board/filesystem with this patch:
> 27: 1027 0 WUGEN 13 Level omap-dma-engine
>
> Or copying files from SD card to eMCC:
> 2.1G /usr/
> 232001
>
> W/o LinkedList we see ~761069 DMA interrupts.
> With LinkedList support it is down to ~269314 DMA interrupts.
>
> With the decreased DMA interrupt number the CPU load is dropping
> significantly as well.
Interesting, I would have counted the throughput of DMA by using time for
transfer and not really interrupts and CPU load. With LL mode, you get a
big performance boost due to starting next transaction by hardware without
waiting for CPU intervention and yes side effect is lesser interrupts and
load :)
> @@ -743,6 +863,7 @@ static struct dma_async_tx_descriptor *omap_dma_prep_slave_sg(
> struct omap_desc *d;
> dma_addr_t dev_addr;
> unsigned i, es, en, frame_bytes;
> + bool ll_failed = false;
> u32 burst;
>
> if (dir == DMA_DEV_TO_MEM) {
> @@ -818,16 +939,47 @@ static struct dma_async_tx_descriptor *omap_dma_prep_slave_sg(
> */
> en = burst;
> frame_bytes = es_bytes[es] * en;
> +
> + if (sglen >= 2)
> + d->using_ll = od->ll123_supported;
No upperbound on length? Does the hardware support any lengths?
--
~Vinod
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