From mboxrd@z Thu Jan 1 00:00:00 1970 From: "David S. Miller" Subject: Re: [RFC] Use RCU for tcp_ehash lookup Date: Wed, 1 Sep 2004 22:45:46 -0700 Sender: netdev-bounce@oss.sgi.com Message-ID: <20040901224546.03765c8d.davem@davemloft.net> References: <20040831125941.GA5534@in.ibm.com> <20040831135419.GA17642@wotan.suse.de> <20040901113641.GA3918@in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: ak@suse.de, davem@redhat.com, netdev@oss.sgi.com, linux-kernel@vger.kernel.org, dipankar@in.ibm.com, paulmck@us.ibm.com Return-path: To: vatsa@in.ibm.com In-Reply-To: <20040901113641.GA3918@in.ibm.com> Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org On Wed, 1 Sep 2004 17:06:41 +0530 Srivatsa Vaddagiri wrote: > On Tue, Aug 31, 2004 at 03:54:20PM +0200, Andi Kleen wrote: > > I bet also when you just do rdtsc timing for the TCP receive > > path the cycle numbers will be way down (excluding the copy). > > I got cycle numbers for the lookup routine (with CONFIG_PREEMPT turned off). > They were taken on a 900MHz 8way Intel P3 SMP box. The results are as below: > > > ------------------------------------------------------------------------------- > | 2.6.8.1 | 2.6.8.1 + my patch > ------------------------------------------------------------------------------- > Average cycles | | > spent in | | > __tcp_v4_lookup_established | 2970.65 | 668.227 > | (~3.3 micro-seconds) | (~0.74 microseconds) > ------------------------------------------------------------------------------- > > This repesents improvement by a factor of 77.5%! And yet none of your benchmarks show noticable improvements, which means that this micro-measurement is totally unimportant in the grand scheme of things as far as we know. I'm not adding in a patch that merely provides some micro-measurement improvement that someone can do a shamans dance over. :) If we're going to add this new level of complexity to the TCP code we need to see some real usage performance improvement, not just something that shows up when we put a microscope on a single function.