Re: [RFC] Use RCU for tcp_ehash lookup
From: "David S. Miller" <davem@davemloft.net>
Date: 2004-09-02 05:49:49
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On Wed, 1 Sep 2004 17:06:41 +0530 Srivatsa Vaddagiri [off-list ref] wrote:
On Tue, Aug 31, 2004 at 03:54:20PM +0200, Andi Kleen wrote:quoted
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.