From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751211AbcHHFes (ORCPT ); Mon, 8 Aug 2016 01:34:48 -0400 Received: from mga01.intel.com ([192.55.52.88]:47232 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750798AbcHHFeq (ORCPT ); Mon, 8 Aug 2016 01:34:46 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.28,488,1464678000"; d="scan'208";a="745614565" Date: Mon, 8 Aug 2016 11:12:26 +0530 From: Vinod Koul To: Peter Ujfalusi Cc: linux@arm.linux.org.uk, linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-omap@vger.kernel.org, tony@atomide.com Subject: Re: [PATCH v2 6/6] dmaengine: omap-dma: Support for LinkedList transfer of slave_sg Message-ID: <20160808054226.GR9681@localhost> References: <20160720085032.2955-1-peter.ujfalusi@ti.com> <20160720085032.2955-7-peter.ujfalusi@ti.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160720085032.2955-7-peter.ujfalusi@ti.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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