From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steve Wise Subject: Re: [openib-general] [PATCH v4 01/13] Linux RDMA Core Changes Date: Thu, 04 Jan 2007 15:49:31 -0600 Message-ID: <1167947371.3071.59.camel@stevo-desktop> References: <1167851839.4187.36.camel@stevo-desktop> <20070103193324.GD29003@mellanox.co.il> <1167855618.4187.65.camel@stevo-desktop> <1167859320.4187.81.camel@stevo-desktop> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: "Michael S. Tsirkin" , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, openib-general@openib.org Return-path: Received: from rrcs-24-153-217-226.sw.biz.rr.com ([24.153.217.226]:55473 "EHLO smtp.opengridcomputing.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030191AbXADVtb (ORCPT ); Thu, 4 Jan 2007 16:49:31 -0500 To: Roland Dreier In-Reply-To: Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Thu, 2007-01-04 at 13:34 -0800, Roland Dreier wrote: > OK, I'm back from vacation today. > > Anyway I don't have a definitive statement on this right now. I guess > I agree that I don't like having an extra parameter to a function that > should be pretty fast (although req notify isn't quite as hot as > something like posting a send request or polling a cq), given that it > adds measurable overhead. (And I am surprised that the overhead is > measurable, since 3 arguments still fit in registers, but OK). > > I also agree that adding an extra entry point just to pass in the user > data is ugly, and also racy. > > Giving the kernel driver a pointer it can read seems OK I guess, > although it's a little ugly to have a backdoor channel like that. > > I'm somewhat surprised the driver has to go into the kernel to rearm a > CQ -- what makes the operation need kernel privileges? (Sorry for not > reading the code) > - Rearming the CQ requires reading and writing to a global adapter register that is shared and thus needs to be protected. They didn't architect the rearm to be a direct user operation. Steve.