The different realtime kernels

Thu Sep 30 19:00:33 BST 2010

Am pleased to see confidence being expressed. But I've yet for the first
time, hear sound, produce a video or hear good music from my PC using ubuStu
10.04.1 lts on my ASUS 64AMD or on my Acer Laptop via UbuStu found on it; am
having to ask others to do what geeks patiently make feasible. But a
non-geek like me wants to believe, I am ever so close to realizing. Keep up
the fight; I support you and will stick in here too believing it is okay to
use my OS solely to crunch words. Yes I hope I will be producing DVDs
showing work I and friends do instead of just wishing I/we could. Million
thanks! Just do not stop perfecting end products! Ken

On Thu, Sep 30, 2010 at 10:55 AM, Ralf Mardorf
<ralf.mardorf at alice-dsl.net>wrote:

> On Thu, 2010-09-30 at 17:45 +0200, Ralf Mardorf wrote:
> > Hi Ricardo :)
> >
> > sorry for my broken English, especially at the moment, because I do have
> > an influenza.
> >
> > On Thu, 2010-09-30 at 16:18 +0100, Ricardo Lameiro wrote:
> > > Hi Ralf,
> > >
> > > I didn't understood what did you meant with:
> > > > For what do multimedia users (producers, but consumers) need more,
> > > but
> > > > vanilla + rt-patch? Does somebody run a multi-user data server on
> > > the
> > > > same machine, as he is using in his audio or audio-video studio?
> > > This
> > > > would be nonsense.
> > >
> > > What would be nonsense? audio producers using hard RT preemption on
> > > the kernel?
> > > Do you think that a webserver needs more Realtime preemption than
> > > audio work?
> >
> > No, I guess for audio and audio-video productions we only need a vanilla
> > + rt-patch kernel and nothing more.
> >
> > Nobody should run a web-server or anything else on a DAW, so there are
> > no other kernel patches needed.
> >
> > I'm pro PREEMPT RT and against PREEMPT only ;) or any kernel patches
> > that don't make sense for audio, audio-video productions.
> >
> > I was asking for reasons to patch a kernel with something like a
> > 'generic'-patch. A DAW, resp. audio-video-MIDI workstation don't need a
> > special server-kernel, or desktop-kernel etc., just a vanilla kernel +
> > rt-patch.
> >
> > Why does Ubuntu Studio comes without PREEMPT RT, but just PREEMPT?!
> > This is my intension.
> >
> > FWIW, I'm a professional audio and video engineer and did program oldish
> > computers and I'm missing hard real-time for modern PCs. Even the
> > kernel-rt isn't able to do hard real-time, so I don't understand why
> > Ubuntu Studio does prefer a kernel without rt-patch. Today the rt-patch
> > isn't good enough
>
> PS:
>
> Pardon, it isn't good enough for all needs, but good for a lot of needs,
> hence we should use the rt-patch.
>
> > and any kernel without this patch is useless for
> > multimedia production.
> >
> > So a misunderstanding ;)!
> >
> > >
> > > As I see, If a webserver used a RT kernel, it would have a lot of
> > > problems, because it will probably lock in some tasks until they are
> > > finished.
> > >
> > > Audio needs a very low latency, high resolution timer etc, because the
> > > Interrupts given by sound cards and by audio software need to be
> > > addressed as fast as possible,
> >
> > This is what I'm thinking off, I sometimes use the hr timer, that on
> > Linux still is a PITA on some machines and for some apps.
> >
> > Anyway, if possible a multimedia distro should use hr timer (HPET), but
> > always a kernel-rt only.
> >
> > >  if they arent, what happens is that the audio buffers, either for the
> > > souncard playback, or capture will run out of data, and then the
> > > continuos steam of audio data will be over, and wait until receive
> > > more info. In a Nutshell, you LOSE audio data, and you will never get
> > > it back, for professional audio that is unacceptable. Also if You give
> > > software RT priorities, it less possible that, for instance, Ardour is
> > > left behind of a twitter client.... unaceptable to...
> > >
> > > I am going to make some simple math with a not so professional cenario
> > > to ilstrate just the data stream, not audo software CPU time.
> > >
> > >
> > > Recording and monitoring out 8 channels (8 in 8 out) at 48KS/s at 24
> > > bits
> > >
> > > 48000 * 24 = 115200 bps = 14.0625KB/s
> > >
> > > 14.0625 * 16 = 225 KB/s = 1.76MB/s
> > >
> > > Well, 1.76 MB/s is not to much really, well this calc is simple
> > > cenario, provided that the sound card uses real 24 bit audio data
> > > stream, if it used 32 bit, welll do the math.
> > >
> > > Now to a PRO setup.. 192 KS/s @ 24bits
> > >
> > > 192000 * 24 = 4608000 = 0.55 MB/s
> > >
> > > 0.55 * 16  = 8,78 MB/s
> > >
> > > 8.78 MBytes per second, not mbits, FIrewire is rated at 400 MBit per
> > > second... USB in practice is a lot less + Communication overhead.
> > >
> > > This is only on the Audio tranfer side, then you need to send this
> > > streams from each different software, make dsp calculations for
> > > Amplitude (volume) or mixing. This takes time.... so YES a Real time
> > > kernels is better for audio users than for normal users. Specially if
> > > you use Externals Firewire/USB card with high outputs
> > >
> > > note: this are simple calculations made fast, just to demonstrate the
> > > kind of stream we talk about. I assumed 24 bits, this is very rare,
> > > usually it goes with 32 bit, that is a lot more data to transfer.
> > >
> > > If some more explanation on why a RT kernel is prefered for audio, i
> > > can try to answer some more questions, i am not a pro in this tough.
> > >
> > > Ricardo Lameiro
> > >
> > > 2010/9/30 Ralf Mardorf <ralf.mardorf at alice-dsl.net>
> > >
> > >         On Thu, 2010-09-30 at 16:38 +0200, Ralf Mardorf wrote:
> > >         > On Thu, 2010-09-30 at 07:35 -0400, Ronan Jouchet wrote:
> > >         > > Hello everybody,
> > >         > >
> > >         > > Many are confused about the various realtime kernels, so
> > >         here is a
> > >         > > reminder of the situation as of Sept. 2010 (but _please_
> > >         see
> > >         > >
> > >         https://help.ubuntu.com/community/UbuntuStudio/RealTimeKernel, which is
> > >         > > more detailed and continuously updated).
> > >         > >
> > >         > > ***Summary***
> > >         > > vanilla = unpatched kernel straight from kernel.org
> > >         > > generic = vanilla + ubuntu sauce (it's the default ubuntu
> > >         kernel)
> > >         > >
> > >         > > The *soft realtime kernels, prepared by changing
> > >         build-time parameters*
> > >         > >      preempt = generic + mild configuration to reduce
> > >         latency
> > >         > >      lowlatency = generic + aggressive configuration to
> > >         reduce latency
> > >         > >
> > >         > > The *hard realtime kernels, prepared by applying a big
> > >         patch* from Ingo
> > >         > > Molnar to the kernel source before building:
> > >         > >      realtime = vanilla + patch (hard to maintain and
> > >         stabilize because
> > >         > > merging 2 pieces of code is never easy)
> > >         > >      rt = generic + patch (even harder to maintain and
> > >         stabilize because
> > >         > > merging 3 pieces of code is harder than 2)
> > >         > >
> > >         > > ***Availability***
> > >         > > - for Maverick, generic will be the only kernel in the
> > >         archives, thus
> > >         > > the default kernel for ubuntu and ubuntustudio, but
> > >         Alessio has been
> > >         > > maintaining a PPA providing lowlatency and realtime
> > >         > > - for Natty or later: work is being done to include
> > >         lowlatency in the
> > >         > > official archives and make it the default ubuntustudio
> > >         kernel
> > >         > >
> > >         > > I hope this clears some doubts. By the way, this confusion
> > >         is only going
> > >         > > to get more intense at release time (less informed /
> > >         technical users).
> > >         > > Could we include some kind of note informing users about
> > >         this? Why not a
> > >         > > "RealTime kernel help" item in the Audio Production menu,
> > >         redirecting to
> > >         > > the wiki page?
> > >         > >
> > >         > > Good day,
> > >         > >
> > >         > > -- Ronan Jouchet
> > >         >
> > >
> > >         >
> > >         > 2 cents,
> > >         > Ralf
> > >
> > >
> > >         PS: Ok, on 32-bit architecture some might need support for
> > >         large RAM in
> > >         addition, this might be an additional patch, hat's not needed
> > >         on 64-bit
> > >         architecture.
> > >
> > >
> > >
> > >         --
> > >         Ubuntu-Studio-users mailing list
> > >         Ubuntu-Studio-users at lists.ubuntu.com
> > >         Modify settings or unsubscribe at:
> > >         https://lists.ubuntu.com/mailman/listinfo/ubuntu-studio-users
> > >
> > >
> > >
> > >
> > > --
> > > Fagote / Contrafagote
> > > Bassoon / Contra-bassoon
> > > http://myspace.com/ricardolameiro
> >
>
>
>
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