From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH v2 0/3] iommu: Avoid DMA ops domain refcount contention Date: Fri, 14 Sep 2018 13:48:59 +0100 Message-ID: <20180914124858.GA4010@arm.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Robin Murphy Cc: catalin.marinas-5wv7dgnIgG8@public.gmane.org, guohanjun-hv44wF8Li93QT0dZR+AlfA@public.gmane.org, linuxarm-hv44wF8Li93QT0dZR+AlfA@public.gmane.org, iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, hch-jcswGhMUV9g@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: iommu@lists.linux-foundation.org Hi Robin, On Wed, Sep 12, 2018 at 04:24:11PM +0100, Robin Murphy wrote: > John raised the issue[1] that we have some unnecessary refcount contention > in the DMA ops path which shows scalability problems now that we have more > real high-performance hardware using iommu-dma. The x86 IOMMU drivers are > sidestepping this by stashing domain references in archdata, but since > that's not very nice for architecture-agnostic code, I think it's time to > look at a generic API-level solution. > > These are a couple of quick patches based on the idea I had back when > first implementing iommu-dma, but didn't have any way to justify at the > time. However, the reports of 10-25% better networking performance on v1 > suggest that it's very worthwhile (and far more significant than I ever > would have guessed). > > As far as merging goes, I don't mind at all whether this goes via IOMMU, > or via dma-mapping provided Joerg's happy to ack it. I think it makes most sense for Joerg to take this series via his tree. Anyway, I've been running them on my TX2 box and things are happy enough, so: Tested-by: Will Deacon Will