On Sat, Oct 24, 2015 at 11:57:53AM +0200, Robert Jarzmik wrote: > Robert Jarzmik <robert.jarzmik@xxxxxxx> writes: > > > This patch attempts to enhance the case of a transfer submitted multiple > > times, and where the cost of creating the descriptors chain is not > > negligible. > > > > This happens with big video buffers (several megabytes, ie. several > > thousands of linked descriptors in one scatter-gather list). In these > > cases, a video driver would want to do : > > - tx = dmaengine_prep_slave_sg() > > - dma_engine_submit(tx); > > - dma_async_issue_pending() > > - wait for video completion > > - read video data (or not, skipping a frame is also possible) > > - dma_engine_submit(tx) > > => here, the descriptors chain recalculation will take time > > => the dma coherent allocation over and over might create holes in > > the dma pool, which is counter-productive. > > - dma_async_issue_pending() > > - etc ... > > > > In order to cope with this case, virt-dma is modified to prevent freeing > > the descriptors upon completion if DMA_CTRL_REUSE flag is set in the > > transfer. > > > > This patch is a respin of the former DMA_CTRL_ACK approach, which was > > reverted due to a regression in audio drivers. > > > > Signed-off-by: Robert Jarzmik <robert.jarzmik@xxxxxxx> > > --- > > Since v1: added doxygen commit to vchan_tx_desc_free > > Hi Vinod, > > Is this serie good for you or do you have remaining comments to be addressed ? Hi Robert, This series looks good, but I am afraid we are very close to merge window I would like this to be deffered to next one for more stabililty tests and coverage I have pushed this to topic/test/desc_reuse now. This will be in -next after merge window Thanks for fixing this up -- ~Vinod -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
