From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Woodhouse, David" Subject: Re: [PATCH 2/4] iommu: add a bitmap based dma address allocator Date: Wed, 25 Nov 2015 16:40:00 +0000 Message-ID: <1448469599.44976.134.camel@intel.com> References: <4c0804c85404be81acfe81fcd402f1af484e9d5f.1448401089.git.shli@fb.com> <1448402209.44976.109.camel@intel.com> <20151124220511.GA2106568@devbig084.prn1.facebook.com> <20151125144613.GA3763@suse.de> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============3544065951122863941==" Return-path: In-Reply-To: <20151125144613.GA3763-l3A5Bk7waGM@public.gmane.org> Content-Language: en-GB 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: "jroedel-l3A5Bk7waGM@public.gmane.org" , Shaohua Li Cc: "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , "Kernel-team-b10kYP2dOMg@public.gmane.org" List-Id: iommu@lists.linux-foundation.org --===============3544065951122863941== Content-Language: en-GB Content-Type: multipart/signed; micalg=sha-1; protocol="application/x-pkcs7-signature"; boundary="=-iBVvVC+TLBrKumlO7DS+" --=-iBVvVC+TLBrKumlO7DS+ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2015-11-25 at 15:46 +0100, jroedel-l3A5Bk7waGM@public.gmane.org wrote: > 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 want= s > > to do it, but I think this shouldn't be a blocker for these patches > > giving it has huge performance gain. >=20 > 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? A percpu lock doesn't bounce cachelines between CPUs very much, so from that point of view it might as well not exist :) --=20 Sent with Evolution's ActiveSync support. 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