From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bart Van Assche Subject: Re: [PATCH v1 00/16] NFS/RDMA patches proposed for 4.1 Date: Wed, 6 May 2015 09:01:07 +0200 Message-ID: <5549BC33.30905@sandisk.com> References: <20150313211124.22471.14517.stgit@manet.1015granger.net> <20150505154411.GA16729@infradead.org> <5E1B32EA-9803-49AA-856D-BF0E1A5DFFF4@oracle.com> <20150505172540.GA19442@infradead.org> <55490886.4070502@talpey.com> <20150505191012.GA21164@infradead.org> <55492ED3.7000507@talpey.com> <20150505210627.GA5941@infradead.org> <554936E5.80607@talpey.com> <20150505223855.GA7696@obsidianresearch.com> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20150505223855.GA7696-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Jason Gunthorpe , Tom Talpey Cc: Christoph Hellwig , Chuck Lever , Linux NFS Mailing List , linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-rdma@vger.kernel.org On 05/06/15 00:38, Jason Gunthorpe wrote: > Heck, on modern systems 100% of these requirements can be solved just > by using the IOMMU. No need for the HCA at all. (HCA may be more > performant, of course) Hello Jason, Any performance tests I have run so far with the IOMMU enabled show much worse results than the same test with the IOMMU disabled. The perf tool learned me that this performance difference is due to lock contention caused by the IOMMU kernel code. I have not yet tried to verify whether this is an implementation issue or something fundamental. This is why I'm not enthusiast about any approach that relies on the IOMMU being enabled. Bart. -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html