From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steve Modica Subject: Re: Tigon3 5701 PCI-X recv performance problem Date: Wed, 08 Oct 2003 13:21:50 -0500 Sender: netdev-bounce@oss.sgi.com Message-ID: <3F8455BE.8080300@sgi.com> References: <3F844578.40306@sgi.com> <20031008101046.376abc3b.davem@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Cc: johnip@sgi.com, netdev@oss.sgi.com, jgarzik@pobox.com, jes@sgi.com Return-path: To: "David S. Miller" In-Reply-To: <20031008101046.376abc3b.davem@redhat.com> Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org David S. Miller wrote: > Oh yeah? What are your numbers like if you just disable the ia64 > kernel unaligned access printk()? Hi David, it's definitely not the printk. They have that throttled so it only prints once for a large number of occurances. The problem is that on the Altix platform they have to deal with unaligned accesses via an exception handler. This causes them to run through hundreds of instructions. There's evidntally another mechanism in the cpu that's more efficient in daling with unaligned accesses, but we can't use that for some reason (atomicity I think, but I don't recall). This extra memcpy when the buffer is not unaligned currently only impacts 5701 (since it's the only chip for which the 2 byte pad is omitted) although the alignment issue would bite us no matter what the chip if the 2 byte pad is omitted. Steve -- Steve Modica work: 651-683-3224 MTS-Technical Lead "Give a man a fish, and he will eat for a day, hit him with a fish and he leaves you alone" - me