On 08/08/16 08:42, Vinod Koul wrote:
> 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 :)
I did throughput test as well, it was slightly faster, but not the boost I was
hoping for.
The copy of the /usr (2.1G) - 5 runs average:
w/o linked list: 7:30 mins
with this patch: 7:23 mins
The limiting factor here is the SD card I have used. But the board was way
more responsible during heavy I/O tasks, like running 'emerge --sync' I can
still use the board.
>> @@ -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?
No, we don't have upper limit, we can link as many sg as we could allocate
from the pool.
--
Péter
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