From owner-freebsd-arch@FreeBSD.ORG Wed Sep 19 00:33:49 2007 Return-Path: Delivered-To: arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id BB3FC16A41A for ; Wed, 19 Sep 2007 00:33:49 +0000 (UTC) (envelope-from sam@errno.com) Received: from ebb.errno.com (ebb.errno.com [69.12.149.25]) by mx1.freebsd.org (Postfix) with ESMTP id 59A3413C428 for ; Wed, 19 Sep 2007 00:33:49 +0000 (UTC) (envelope-from sam@errno.com) Received: from trouble.errno.com (trouble.errno.com [10.0.0.248]) (authenticated bits=0) by ebb.errno.com (8.13.6/8.12.6) with ESMTP id l8INUGaf029610 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Tue, 18 Sep 2007 16:30:16 -0700 (PDT) (envelope-from sam@errno.com) Message-ID: <46F05F88.5060809@errno.com> Date: Tue, 18 Sep 2007 16:30:16 -0700 From: Sam Leffler User-Agent: Thunderbird 2.0.0.6 (X11/20070814) MIME-Version: 1.0 To: Jeff Roberson References: <20070917165657.B558@10.0.0.1> <46EF644E.9050207@elischer.org> <20070918012555.G558@10.0.0.1> <46EFE4BD.4030505@freebsd.org> <20070918142115.C558@10.0.0.1> <20070918153536.D558@10.0.0.1> In-Reply-To: <20070918153536.D558@10.0.0.1> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-DCC--Metrics: ebb.errno.com; whitelist Cc: arch@freebsd.org, Andre Oppermann , Julian Elischer Subject: Re: 64bit ticks, was Re: Changing p_swtime and td_slptime to ticks X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 19 Sep 2007 00:33:49 -0000 Jeff Roberson wrote: > On Tue, 18 Sep 2007, Jeff Roberson wrote: > >> On Tue, 18 Sep 2007, Andre Oppermann wrote: >> >>> Jeff Roberson wrote: >>>> On Mon, 17 Sep 2007, Julian Elischer wrote: >>>> >>>>> Jeff Roberson wrote: >>>>>> Enclosed is a patch that fixes swapping with ULE. ULE has never >>>>>> properly set p_swtime and td_slptime which are used by the >>>>>> swapout/swapin code to select the appropriate thread to swap. >>>>> >>>>> I have not looked at in the depth required, but 2 points that I >>>>> was unable >>>>> to check to my satisfaction before I got called away for work.... >>>>> >>>>> 1/ the source of the ticks is a monotonically increasing count >>>>> that never >>>>> goes backwards or changes? >>>> >>>> ticks is incremented each time hardclock() is called. That's it. >>>> >>>>> >>>>> 2/ nothing that used to be accounted in seconds becomes accounted >>>>> for in ticks? >>>> >>>> I scale back to seconds where it is required. Really I think ticks >>>> would be the better metric in vm_glue.c but didn't want to make any >>>> drastic changes. >>> >>> ticks is 2^31 on x86 and at HZ=1000 is wraps within a reasonable >>> short uptime. You have to make sure that your code handles that >>> correctly or you run into lots of strange effects which are almost >>> impossible to reproduce. In TCP we've got bitten by that. >> >> Thanks Andre, this is a good point. For the td_slptime I don't think >> it's of practical concern. However, for swtime I think I will >> convert it then to seconds from boot. > > Is there a good reason for not making ticks 64bit? math involving > this value is relatively infrequent. Bruce? Any comments? It'd sure > let us forget all of these counter wrapping problems. ticks is used a lot. I'd rather set hz back to 100 by default. This approach is a perfect example of ignoring low-end platforms. Sam