From owner-freebsd-hackers@FreeBSD.ORG Wed Oct 3 03:22:43 2007 Return-Path: Delivered-To: hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 155E016A418; Wed, 3 Oct 2007 03:22:43 +0000 (UTC) (envelope-from bright@elvis.mu.org) Received: from elvis.mu.org (elvis.mu.org [192.203.228.196]) by mx1.freebsd.org (Postfix) with ESMTP id 0A09D13C4B7; Wed, 3 Oct 2007 03:22:42 +0000 (UTC) (envelope-from bright@elvis.mu.org) Received: by elvis.mu.org (Postfix, from userid 1192) id DC8F41A4D7E; Tue, 2 Oct 2007 20:22:42 -0700 (PDT) Date: Tue, 2 Oct 2007 20:22:42 -0700 From: Alfred Perlstein To: Daniel Eischen Message-ID: <20071003032242.GR31826@elvis.mu.org> References: <20071003015231.GJ31826@elvis.mu.org> <20071003025418.GN31826@elvis.mu.org> <20071003030943.GQ31826@elvis.mu.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.3i Cc: hackers@freebsd.org Subject: Re: Critical Sections for userland. X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 03 Oct 2007 03:22:43 -0000 * Daniel Eischen [071002 20:16] wrote: > On Tue, 2 Oct 2007, Alfred Perlstein wrote: > > >* Daniel Eischen [071002 20:02] wrote: > >>On Tue, 2 Oct 2007, Alfred Perlstein wrote: > >> > >>>* Daniel Eischen [071002 19:46] wrote: > >>>>On Tue, 2 Oct 2007, Alfred Perlstein wrote: > >>>> > >>>>>Hi guys, we need critical sections for userland here. > >>>>> > >>>>>This is basically to avoid a process being switched out while holding > >>>>>a user level spinlock. > >>>> > >>>>Setting the scheduling class to real-time and using SCHED_FIFO > >>>>and adjusting the thread priority around the lock doesn't work? > >>> > >>>Too heavy weight, we want to basically have this sort of code > >>>in userland: > >> > >>Well, yeah, but are you _really_ sure that you aren't just > >>running something that should be real-time and have priority > >>over other applications? SCHED_FIFO means you will run until > >>you relinquish the CPU (you can only do this as root). If > >>all your threads are well behaved, would this work? Have > >>you tried it? > > > >No, because it wouldn't work. How do we know when to let go > >of the cpu? In my system, the kernel tells you without polling. > > You don't have to know when to "let go of the cpu" if your > threads are well behaved (meaning they block on some event, > or have periods when they wait). They will let go of the > CPU normally. When they're busy, they will not be switched > out (unless perhaps there is an interrupt thread that needs > to run -- I'm not sure how real-time threads get scheduled > against ithreads). > > If your threads are not well behaved (CPU hogs), then that > isn't going to work because they'll probably bog down the > system. Yes, I know how threading works. Unfortunately, your solution is not workable for us. thank you, -- - Alfred Perlstein