From mboxrd@z Thu Jan 1 00:00:00 1970 From: Or Gerlitz Subject: Re: decent performance drop for SCSI LLD / SAN initiator when iommu is turned on Date: Tue, 7 May 2013 15:12:29 +0300 Message-ID: <5188EFAD.50708@mellanox.com> References: <20130502015603.GC26105@redhat.com> <5188304E.9050603@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5188304E.9050603-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Alexander Duyck Cc: Or Gerlitz , "Michael S. Tsirkin" , Roland Dreier , iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, Yan Burman , linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Paolo Bonzini , Asias He List-Id: linux-rdma@vger.kernel.org On 07/05/2013 01:35, Alexander Duyck wrote: > The Tx path ends up taking a performance hit if IOMMU is enabled. It > just isn't as severe due to things like TSO. In testing done by some Mellanox folks I think they see major penalty on the RX side, but hardly nothing on the TX side, I'll check that. > One way to work around the performance penalty is to allocate bounce > buffers and just leave them static mapped. Then you can simply memcpy > the data to the buffers and avoid the locking overhead of > allocating/freeing IOMMU resources. It consumes more memory but works > around the IOMMU limitations. I don't think can be applicable approach to fast networking/storage drivers. Or. -- 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