From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753354AbcGSMgB (ORCPT ); Tue, 19 Jul 2016 08:36:01 -0400 Received: from arroyo.ext.ti.com ([198.47.19.12]:51985 "EHLO arroyo.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752419AbcGSMf7 (ORCPT ); Tue, 19 Jul 2016 08:35:59 -0400 Subject: Re: [PATCH 2/7] dmaengine: omap-dma: Complete the cookie first on transfer completion To: Russell King - ARM Linux References: <20160714124242.7579-1-peter.ujfalusi@ti.com> <20160714124242.7579-3-peter.ujfalusi@ti.com> <20160718103409.GH5783@n2100.arm.linux.org.uk> CC: , , , , , From: Peter Ujfalusi Message-ID: <923b54d6-c7fc-66c2-1c20-d8d74ebed912@ti.com> Date: Tue, 19 Jul 2016 15:35:18 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: <20160718103409.GH5783@n2100.arm.linux.org.uk> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/18/16 13:34, Russell King - ARM Linux wrote: > On Thu, Jul 14, 2016 at 03:42:37PM +0300, Peter Ujfalusi wrote: >> Before looking for the next descriptor to start, complete the just finished >> cookie. > > This change will reduce performance as we no longer have an overlap > between the next request starting to be dealt with in the hardware > vs the previous request being completed. vchan_cookie_complete() will only mark the cookie completed, adds the vd to the desc_completed list (it was deleted from desc_issued list when it was started by omap_dma_start_desc) and schedule the tasklet to deal with the real completion later. Marking the just finished descriptor/cookie done first then looking for possible descriptors in the queue to start feels like a better sequence. After a quick grep in the kernel source: only omap-dma.c was starting the next transfer before marking the current completed descriptor/cookie done. > Your commit log doesn't > say _why_ the change is being made, it merely tells us what the > patch is doing, which we can see already. > > Please describe changes a little better. > -- Péter