From owner-freebsd-current@FreeBSD.ORG Wed Nov 21 00:08:05 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 6DBA016A41A; Wed, 21 Nov 2007 00:08:05 +0000 (UTC) (envelope-from jroberson@chesapeake.net) Received: from webaccess-cl.virtdom.com (webaccess-cl.virtdom.com [216.240.101.25]) by mx1.freebsd.org (Postfix) with ESMTP id 2DDDE13C45A; Wed, 21 Nov 2007 00:08:05 +0000 (UTC) (envelope-from jroberson@chesapeake.net) Received: from [192.168.1.107] (cpe-24-94-75-93.hawaii.res.rr.com [24.94.75.93]) (authenticated bits=0) by webaccess-cl.virtdom.com (8.13.6/8.13.6) with ESMTP id lAL07LbZ042150; Tue, 20 Nov 2007 19:07:22 -0500 (EST) (envelope-from jroberson@chesapeake.net) Date: Tue, 20 Nov 2007 14:08:49 -1000 (HST) From: Jeff Roberson X-X-Sender: jroberson@192.168.1.107 To: Kris Kennaway In-Reply-To: <4743342A.10507@FreeBSD.org> Message-ID: <20071120140752.C884@192.168.1.107> References: <20071120141403.GE81260@comp.chem.msu.su> <4743342A.10507@FreeBSD.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Cc: Yar Tikhiy , 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: Wed, 21 Nov 2007 00:08:05 -0000 On Tue, 20 Nov 2007, Kris Kennaway wrote: > 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. I definitely knew about problems with positively niced tasks. I had not heard about the negative nice problems. This is my top priority as far as opensource goes. I've been unfortunately busy with other things however. I hope to get to this soon. Thanks, Jeff > > Kris > _______________________________________________ > freebsd-current@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-current > To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org" >