From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: linux-rt-users-owner@vger.kernel.org Received: from barracuda2.shentel.net ([204.111.1.145]:38988 "EHLO barracuda4.shentel.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728617AbeHWRO5 (ORCPT ); Thu, 23 Aug 2018 13:14:57 -0400 Received: from smtp1.edbg.cloud.shentel.net (smtp1.edbg.cloud.shentel.net [204.111.2.17]) by barracuda4.shentel.net with ESMTP id 8XacAh2cDOzqrysV for ; Thu, 23 Aug 2018 09:45:02 -0400 (EDT) Received: from coyote.coyote.den (unknown [204.111.64.149]) by smtp1.edbg.cloud.shentel.net (Postfix) with ESMTPSA id D70522248A for ; Thu, 23 Aug 2018 09:45:02 -0400 (EDT) From: Gene Heskett Subject: Re: SCHED_DEADLINE as user Date: Thu, 23 Aug 2018 09:45:02 -0400 References: <20180823123739.GC31443@localhost.localdomain> <20180823150040.7da1624f@luca64> In-Reply-To: <20180823150040.7da1624f@luca64> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <201808230945.02854.gheskett@shentel.net> Sender: linux-rt-users-owner@vger.kernel.org List-ID: To: linux-rt-users@vger.kernel.org On Thursday 23 August 2018 09:00:40 luca abeni wrote: > On Thu, 23 Aug 2018 14:37:39 +0200 > Juri Lelli wrote: > [...] > > > > > Maybe the existing system wide sched_rt_{period, > > > > runtime}_us are enough? > > > > > > I do not know... A cgroup-based interface looks more powerful (and > > > not so difficult to implement... :), and would allow the sysadmin > > > to decide which users can use SCHED_DEADLINE, how much > > > SCHED_DEADLINE bandwidth can each user/group use, etc... > > > > How about extending PAM limits instead? It looks like it's what > > (e.g.) audio users rely on already [1]. It is maybe possible to add > > dlruntime, dlperiod, dldeadline parameters in there? > > Ok, I do not know much about these PAM limits... Where can I find more > information? What do we need to implement exactly, to add these > dlruntime, dlperiod, dldeadline parameters? > > > Thanks, > Luca Are you folks interested in input from a real world user? On who at the moment is building about half these kernels as you announce them on a pi-3b, the same pi-3b running 1500 lbs of a Sheldon 11"x36" lathe. I am running linuxcnc on both x86 and armhf machinery, two lathes and two milling machines, all being moved by stepper motors. Steppers, if the steps are being software generated, are very sensitive to timing wibbles in a stream of steps, with a 5 microsecond wobble in the timing haveing serious effects on the available torque by causing a speedup and slowdown. This severely limits the speed at which the motor can be driven without stalling or losing steps, which in a stepper system is the equivalent of losing its home reference which=wrecked part. I have one machine still depending on software stepping. I could easily triple the speed of that machine by spending another 100 dollars to offload that to an fpga based interface card. As it is the base thread runs at about 28 microseconds. That also represents the granularity of a speed change. So it of late has been relegated to doing very precise work via EDM, which is slow anyway. In short, linuxcnc, and its best rtai kernels can do pergaps 10"/minute whereas the fpga cards can move that same machine at 100 ipm. Any help in getting the latency down means we can do things faster. LinuxCNC is also run as a common user, never as root. Thats my $0.02 from a users viewpoint. -- Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page