From owner-freebsd-current@FreeBSD.ORG Tue Nov 20 19:23:17 2007 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E122216A41A for ; Tue, 20 Nov 2007 19:23:17 +0000 (UTC) (envelope-from kris@FreeBSD.org) Received: from weak.local (pointyhat.freebsd.org [IPv6:2001:4f8:fff6::2b]) by mx1.freebsd.org (Postfix) with ESMTP id 222CF13C447; Tue, 20 Nov 2007 19:23:16 +0000 (UTC) (envelope-from kris@FreeBSD.org) Message-ID: <4743342A.10507@FreeBSD.org> Date: Tue, 20 Nov 2007 20:23:22 +0100 From: Kris Kennaway User-Agent: Thunderbird 2.0.0.9 (Macintosh/20071031) MIME-Version: 1.0 To: Yar Tikhiy References: <20071120141403.GE81260@comp.chem.msu.su> In-Reply-To: <20071120141403.GE81260@comp.chem.msu.su> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: jroberson@chesapeake.net, freebsd-current@freebsd.org Subject: Re: SCHED_ULE & niceness / rtprio X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 20 Nov 2007 19:23:18 -0000 Yar Tikhiy wrote: > Hi all, > > SCHED_ULE seems to do an unfair job to processes with low niceness > or with real-time priority. Here are my observations: > > A few days ago I noticed that music (played by Totem, Gnome's default > player) would pause for a fraction of second each time I did something > in X/Gnome, such as switched between windows, clicked on a link in > the web browser, etc. Then I found that music was jerky only if > the player ran with a negative niceness or a real-time priority: > As soon as I returned it to niceness 0 and normal priority, sound > became totally seamless notwithstanding my activity in X. > > The approximate value required for the effect to appear was niceness > as low as -5 or RT priority as high as 10; niceness -1 or rtprio 1 > wasn't enough. > > Curious, I substituted SCHED_4BSD for SCHED_ULE in my otherwise > GENERIC kernel, and the jerkiness of sound was gone irrespective > of the niceness or RT priority of the player. > > To rule out other possible causes, I also tried kernels with SCHED_ULE > but without SMP or without debug stuff (INVARIANTS+WITNESS), but > the issue was there in both cases, unlike in the case of SCHED_4BSD. > > Of course, X+Gnome+stuff isn't the clearest environment for debugging > schedulers, but multimedia apps are rather sensitive to scheduling > quality. This case should be rather obvious: When I click in an > inactive window, some processes are woken that have been idle. > After that the high-priority player isn't scheduled long enough for > the hardware audo buffer to drain, although it would be scheduled > soon if it had normal priority. > > Did I hit a known issue? Others have reported it, but I don't know if Jeff has had time to investigate yet. Kris