From owner-freebsd-hackers Thu Jan 31 16: 8:58 2002 Delivered-To: freebsd-hackers@freebsd.org Received: from web4.thecenturiongroup.com (112.mujb.nyrk.nycenycp.dsl.att.net [12.98.137.112]) by hub.freebsd.org (Postfix) with ESMTP id 06D2537B405 for ; Thu, 31 Jan 2002 16:08:52 -0800 (PST) Received: from ix1x1000 (ix1x1000.thecenturiongroup.com [192.32.248.52]) by web4.thecenturiongroup.com (Postfix) with SMTP id 4131A7C001; Thu, 31 Jan 2002 18:39:14 -0500 (EST) Message-ID: <005b01c1aaaf$e38ecd70$34f820c0@ix1x1000> From: "Michael Meltzer" To: "Mike Silbersack" , "Storms of Perfection" Cc: , , References: <20020131172729.X38382-100000@patrocles.silby.com> Subject: Re: Clock Granularity (kernel option HZ) Date: Thu, 31 Jan 2002 18:34:55 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2600.0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000 Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG Not knowing but wondering: With Gigabit Ethernet and NFS in the mix, anything that gets latency out is a very good thing :-) and would improve performance. MJM ----- Original Message ----- From: "Mike Silbersack" To: "Storms of Perfection" Cc: ; ; Sent: Thursday, January 31, 2002 12:33 PM Subject: Re: Clock Granularity (kernel option HZ) > > On Thu, 31 Jan 2002, Storms of Perfection wrote: > > > I'm going to benchmark different network senarious with different options > > to see what I can get, and what works best. If someone wants to help me > > out, I could maybe write up a article about it? > > I don't think you'll end up seeing the performance improvements you're > looking for. The case where HZ=1000 is really useful is when using > dummynet; the more accurate scheduling is necessary for it to handle high > data rate pipes properly. > > The TCP stack, on the other hand, is perfectly happy with 10ms resolution. > Retransmission timeouts are only actually used when loss occurs on the > network, and 10ms is more than accurate enough for retransmission. (I > believe that retransmit timeouts are rounded up to 1 second, but don't > quote me on that.) The other timed events (keepalive timeouts, delayed > ack timeouts, etc) are also in good shape with 10ms accuracy. > > So, it's highly unlikely that you'll be able to observe a perceptable > difference in network performance except in really convoluted cases. > > Mike "Silby" Silbersack > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-hackers" in the body of the message To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message