From mboxrd@z Thu Jan 1 00:00:00 1970 From: Martin Devera Subject: Re: [PATCH 0/2] HTB scheduler HTB_HYSTERESIS modifications Date: Wed, 04 Jun 2008 17:31:41 +0200 Message-ID: <4846B55D.4060306@cdi.cz> References: <1212501803.13164.27.camel@localhost.localdomain> <48469323.8000506@cdi.cz> <1212589713.13164.75.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-2; format=flowed Content-Transfer-Encoding: 7bit Cc: "David S. Miller" , "netdev@vger.kernel.org" To: jdb@comx.dk Return-path: Received: from smtp.wifcom.cz ([89.185.251.8]:53290 "EHLO wifcom.cz" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752589AbYFDPcE (ORCPT ); Wed, 4 Jun 2008 11:32:04 -0400 In-Reply-To: <1212589713.13164.75.camel@localhost.localdomain> Sender: netdev-owner@vger.kernel.org List-ID: >> I'm thinking about removing HYSTERESIS code altogether, but >> (and it holds for setting HYSTERESIS=off as default) > > I prefer a turn knob, where the default is off. Ok. As seen from interrupt load below, it is reasonable. > With current testing (on 2.6.25.4) I could not see any changes with CPU > usage, but thats probably caused by the fast CPU on the test system > (Dual Xeon). BUT an interesting observation was that the number of > interrupts increased significantly, from approx 1300 to 2000 per sec. > The other observation was that I got significantly less jitter. Interesting. It is probably result of merging of subsequent yellow/red states without going to green for while. The traffic is more bursty then (it is no longer only timer-granular, but {c,}burst sized bursts are FORCED in output) but NIC driver can emit more outgoing packets per in single "buffer free" interrupt. >> Also, I'm a bit busy for a few weeks, would you be able/interested >> to do such testing ? > > Okay, lets wait until I get this kernel into our real-life production > system. Then I can report on the real-life impact on CPU performance. Thanks, I'll try to set some test up later. With large class-count as state changes will cost more then (RB tree deletes/inserts). Regarding your intr/sec count, what about to keep default value of hysteresis switch as "on" (just to be on safe side) ? I'm afraid what that 40% larger interrupt load might do with bigger routers (I already got some performance related questions from ppl with hundreds classes on 100's Mb links). m.