From mboxrd@z Thu Jan 1 00:00:00 1970 From: "jroedel-l3A5Bk7waGM@public.gmane.org" Subject: Re: [PATCH 2/4] iommu: add a bitmap based dma address allocator Date: Wed, 25 Nov 2015 15:46:13 +0100 Message-ID: <20151125144613.GA3763@suse.de> References: <4c0804c85404be81acfe81fcd402f1af484e9d5f.1448401089.git.shli@fb.com> <1448402209.44976.109.camel@intel.com> <20151124220511.GA2106568@devbig084.prn1.facebook.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20151124220511.GA2106568-tb7CFzD8y5b7E6g3fPdp/g2O0Ztt9esIQQ4Iyu8u01E@public.gmane.org> 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: Shaohua Li Cc: "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , "Kernel-team-b10kYP2dOMg@public.gmane.org" , "Woodhouse, David" List-Id: iommu@lists.linux-foundation.org On Tue, Nov 24, 2015 at 02:05:12PM -0800, Shaohua Li wrote: > The lib/iommu-common.c uses a bitmap and a lock. This implementation > actually uses a percpu_ida which completely avoids locking. It would be > possible to make lib/iommu-common.c use percpu_ida too if somebody wants > to do it, but I think this shouldn't be a blocker for these patches > giving it has huge performance gain. It doesn't "completely avoids locking", the percpu_ida code uses a lock internally too. Also, what is the memory and device address space overhead per cpu? Joerg