On Wed, 2010-07-21 at 15:18 -0300, Bernardo Barros wrote: > Thank you Fernando and David, > > Yes, the person that gave me advise was not an audio oriented guy. > That´s more clear now. > > Just a newbie question here: do you have to determine what programs > will have privileges? How the system knows how to handle taks of audio > and non-audio programs at the same time? You don't have to worry about determining which programs will have privileges (at least directly). If you run Jack with real-time scheduling (if you use Qjackctl you have to set the "Realtime" parameter in "Setup" and the user that is running Jack has to be allowed to use real-time scheduling), then the audio threads within any Jack client will run with real-time scheduling automatically. All other threads in all your programs will run with "normal" scheduling and will have less priority (that includes, for example, graphic i/o threads or file i/o threads in the Jack audio programs - those don't have elevated priority). It is all designed to make sure the chances of an audio glitch happening are as small as possible. -- Fernando > 2010/7/21 Fernando Lopez-Lezcano <nando@xxxxxxxxxxxxxxxxxx>: > > On Wed, 2010-07-21 at 17:35 +0200, David Sommerseth wrote: > >> -----BEGIN PGP SIGNED MESSAGE----- > >> Hash: SHA1 > >> > >> On 19/07/10 18:57, Fernando Lopez-Lezcano wrote: > >> > On Mon, 2010-07-19 at 13:46 -0300, Bernardo Barros wrote: > >> >> > For this low-level task some engineering would be required? I'm not > >> >> > this kind of guy who know much about tasks scheduling and priorities > >> >> > (kernel level) but some people told me that real-time kernels patches > >> >> > could slow down Fedora and I should not use it. > >> > > >> > Did those people by any chance provide you with _numbers_ that tell you > >> > exactly what part of the kernel is impacted and by how much? (and, who > >> > are they?) My guess is probably not. > >> > > >> > Yes, perhaps the rt patches could affect performance. Maybe. In some > >> > subsystems (disk i/o, network come to mind). Maybe by a few %, in some > >> > specific situations. I don't think the impact will be something you will > >> > notice unless you measure it. > >> > >> To put things a bit straight. Yes, RT kernel will affect performance. > >> Point. > > > > Agreed (for the reasons you explain below). > > > > I'd like to add that in the context of real-time performance for audio, > > the lack of an RT kernel will also affect performance for the worse. So, > > it depends on your goals. In the context of this list (music) Bernardo > > comments he got the recommendation to not run RT kernels for performance > > reasons ("some people told me that real-time kernels patches could slow > > down Fedora and I should not use it"). > > > > If you are running a server, don't (unless, of course, you print money > > by running thousands of trades a minute and you need millisecond > > scheduling for that - that is why we have the rt patches after all :-). > > If you are running a music oriented workstation that should handle > > real-time interaction, then I'd say yes, run it. > > > > There are no black and white rules here. If you try the Fedora kernel > > and it works for you in your particular music oriented situation then > > run that. > > > > -- Fernando > > > > > >> Will you notice it effectively on "normal desktop tasks"? Probably not > >> much, but it depends on how your system is saturated, tuned and what > >> kind of loads you have running. Real Time is not Real Fast and never > >> will be. A real time kernel will not give any fair scheduling to your > >> system, basically. > > > > (depends on your definition of "fair", for the purposes of an RT kernel > > it schedules processes fairly, giving the rt tasks priority as is > > intended by design). > > > >> All tasks (processes) which is set to use the SCHED_FIFO or SCHED_RR > >> scheduling, even on the lowest priority will preempt and run it first > >> over, ignoring all other SCHED_OTHER (normal) processes. SCHED_FIFO and > >> SCHED_RR tasks with the highest priority will be processed before all > >> other tasks, whenever they receive signals which requires these > >> processes to run. This is the core nature of a real time system. > >> > >> So if you don't have many SCHED_FIFO or SCHED_RR tasks, and that they > >> are light - you most probably will not notice anything at all. But in > >> the moment you begin with heavy I/O dependent operations or other > >> operations which requires processing time and the kernel have given them > >> SCHED_FIFO scheduling and a rather high priority (which is not > >> uncommon), it will slow down all the other running tasks. But this > >> behaviour is possible to tune! > >> > >> So why would you want to run a real time kernel instead of a so called > >> "real fast" kernel (normal kernels)? Latency determination. A real > >> time kernel will strive to give you a predictable system latency, no > >> matter how loaded your computer is. Which is a key-point for audio and > >> video - you don't want the sound or video stream to be delayed because > >> cron and updatedb wants to run. > >> > >> Some relevant information can be found here: > >> > >> <http://www.redhat.com/docs/en-US/Red_Hat_Enterprise_MRG/1.2/html/Realtime_Installation_Guide/chap-Realtime_Installation_Guide-Why_Use_RT_to_Optimize_Latency.html> > >> > >> > >> <http://www.redhat.com/docs/en-US/Red_Hat_Enterprise_MRG/1.2/html/Realtime_Reference_Guide/index.html> > >> > >> > >> <http://www.redhat.com/docs/en-US/Red_Hat_Enterprise_MRG/1.2/html/Realtime_Tuning_Guide/index.html> > >> > >> > >> kind regards, > >> > >> David Sommerseth > >> -----BEGIN PGP SIGNATURE----- > >> Version: GnuPG v1.4.10 (GNU/Linux) > >> Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org/ > >> > >> iEYEARECAAYFAkxHE9YACgkQIIWEatLf4He6ZwCgjaodaHQY0KJue5TfTZiVhE0d > >> mIEAnRksu5hm9bP6oGUu5ufRh2V1ESt/ > >> =vj0G > >> -----END PGP SIGNATURE----- > >> _______________________________________________ > >> music mailing list > >> music@xxxxxxxxxxxxxxxxxxxxxxx > >> https://admin.fedoraproject.org/mailman/listinfo/music > > > > > > _______________________________________________ music mailing list music@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/music