impact on audio playback on high cpu usage

Sun Jul 25 17:49:25 BST 2010

Hi Duncan,

so i disabled desktop effects, but it didn't help. It's as bad as before. But graphics in general seem to be faster ;)
Pulseaudio is not installed but KDE on Kubuntu depends on libpulse0.

Duncan schrieb am Samstag, 24. Juli 2010 03:59:13:
> Andreas Hennig posted on Fri, 23 Jul 2010 22:34:20 +0200 as excerpted:
> 
> > Hi Duncan,
> > 
> > thanks for your long answer.
> > 
> > So here is some more information.
> > 
> > The CPU is a dual core Intel T2050 @ 1.6GHz.
> 
> Dual-core... really shouldn't be experiencing sound slow-downs with high 
> CPU usage, even @ 1.6 GHz.  I was running dual single-core Opteron 242s in 
> this rig when I first got the mobo.  Those are 1.6 GHz, and as they came 
> out well before any dual-cores did, especially dual-cores for laptops, if 
> anything, clock for clock yours should be better.  Yet even back then, I 
> could run ridiculous load averages (say, several hundred, compiling a 
> kernel) without stuttering -- as long as I wasn't running anything I/O 
> intensive.
> 
> > Since i have a laptop my sondcard is a build in Intel HDA. See lspci:
> > 
> > 00:1b.0 Audio device: Intel Corporation N10/ICH 7 Family High Definition
> > Audio Controller (rev 02)
> 
> Hmm... my netbook runs an ICH-7 chipset. Let me do a quick kernel config 
> and see what sound I run...
> 
> Back on my main machine (the Opteron), in the kernel it's actually the 
> Intel8X0 alsa driver, Intel/Sis/nVidia/AMD/ALi AC97 Controller.  A 
> compatible design was on lots of chipset southbridges, including both AMD 
> (mine) and Intel of the era, but I suspect yours is somewhat newer.
> 
> On the (Intel Atom) netbook, it's the HDA_Intel alsa driver, Intel HD 
> Audio.  lspci says:
> 
> Audio device: Intel Corporation 82801G (ICH7 Family) High Definition Audio 
> Controller (rev 02)
> 
> So the sound controller appears to be the same as on my netbook.  FWIW, 
> I've not noticed any such problems there, even with the rather slower atom 
> single-core (but hyperthreaded, so it appears as two).  However, as it's 
> my portable netbook, not my power workstation, I don't tend to run 
> anything real heavy duty on it.  In particular, I do all my building (I 
> run Gentoo on it too, so all from-source) for it a special 32-bit (it 
> won't do 64-bit, unfortunately) chroot image on my main machine.
> 
> > With Kubuntu 10.4 my desktop efects also seems to be slower. Maybe the
> > grafics driver has been changed. The grafic card is a Radeon Mobility
> > X1400.
> > 
> > lsmod says that i using the radeon driver.
> 
> Well, my netbook obviously uses the built-in Intel 940GM series graphics 
> card, but as I said, my main machine is running Radeon, now an hd4650 
> (r700 series), previously a 9200 (r200 series).  The x1400 is (according 
> to the radeon manpage) the r500 series, so square in between those two.
> 
> The good news is that the r500 series driver is rather more mature than 
> the r600/700 driver that I'm running now, especially good since while I 
> don't see the artifacts on mine I did with the drivers when I first got 
> it, it's still not quite stable and I unfortunately see full system 
> lockups occasionally.  The r500 series driver is mature enough that 
> shouldn't be happening there, altho there might be a few bugs related to 
> kms (kernel mode setting) on it, still, as kms is still new and not fully 
> mature, everywhere.
> 
> One thing that might be happening.  Radeon mobility graphics, as Intel 
> graphics, tend to use shared system memory instead of dedicated graphics 
> memory, saving money and space, but at the cost of performance, since 
> system memory will be slower, and with the usual refresh of 60 Hz or so, 
> is going to be accessing that system memory sixty-times/second, with the 
> CPU therefore unable to use that channel for memory access the same sixty-
> times a second.
> 
> It's /possible/ that with everything going on concurrently, it's 
> impossible to keep the hardware sound buffer full, and that you could see 
> that during high CPU activity, not due to CPU specifically, which as I 
> said shouldn't be happening on a dual-core, but due to the additional 
> stress on the memory bandwidth.
> 
> But I didn't see that you'd tried with compositing toggled off, as I 
> suggested.  Do try it, at least temporarily.  If it doesn't help, if 
> graphics is contributing to the problem, there's probably not a lot we can 
> do about it.  But if it helps, then we know that graphics are involved, 
> and that turning off effects temporarily does help, significantly more 
> than we know now.
> 
> Actually, it may be just me, but I've seen enough complaints about pulse-
> audio, I'm wondering if that's your problem.  I happened to read a recent 
> article on it and Ubuntu, but it was Ubuntu/Gnome, not Kubuntu/KDE, so I 
> don't know how much of it applies to you.  But it's worth taking a look, 
> anyway.
> 
> Direct link:
> http://www.linuxplanet.com/linuxplanet/tutorials/7130/1/
> 
> And here's the Raiden's Realm blurb and link to discussion on the same 
> article. (RR is a friendly linux/gaming/anime/tech related site that I 
> spend a bit of time on.  I have their feed in akregator, and that's where 
> I saw the story originally.  I mostly read the article feed, sometimes 
> commenting on a story, so I don't spend as much time in the forums as I'd 
> like, but as I said, it's friendly, and there's Linux and other forums 
> that may be useful and they're just a nice place to hang out, too. =:^)
> 
> http://www.raiden.net/news/Ubuntu_Tip_Turning_PulseAudio_On_and_Off/
> 
> I'd really suspect that it's pulse-audio, since that extra layer between 
> the apps and alsa is going to be all software and thus CPU usage 
> sensitive, and since I've seen no such issues with the same sound hardware 
> on my supposedly far less powerful atom machine, but there's no way to 
> tell until you try bypassing it, and going to alsa directly.
> 
> Also, no mention yet of whether kde apps (thru phonon) work any better or 
> worse or just the same as non-kde apps.  (I'm not sure but amarok may be 
> able to go to alsa directly, bypassing phonon and possibly bypassing pulse-
> audio.  I know old amarok could, but the new amarok didn't fit my needs so 
> I don't use it any more and uninstalled it.)
> 
> 
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