--Lee Revell <[EMAIL PROTECTED]> wrote (on Tuesday, July 12, 2005 11:00:02 -0400):
> On Tue, 2005-07-12 at 07:56 -0700, Martin J. Bligh wrote: >> --Lee Revell <[EMAIL PROTECTED]> wrote (on Tuesday, July 12, 2005 10:24:59 >> -0400): >> >> > On Mon, 2005-07-11 at 21:30 -0700, Martin J. Bligh wrote: >> >> Exactly what problems >> >> *does* it cause (in visible effect, not "timers are less granular"). >> >> Jittery audio/video? How much worse is it? >> > >> > Yes, exactly. Say you need to deliver a frame of audio or video every >> > 5ms. >> >> Ummm. that's a 200HZ refresh rate, is it not? That seems unreasonable >> (to a lay-person, as far as video goes). >> > > Seems unreasonable now but things like HDTV actually have much tighter > constraints than this. And frame times this small are quite often used > for audio, which admittedly is less affected by HZ because those devices > generate their own interrupts. > >> > You have a rendering thread and a display thread that communicate >> > via FIFOs. The main thread waits in select() for the next frame to >> > complete rendering or for the deadline to expire. That's next to >> > impossible with HZ=100, because the best you can do is the deadline >> > +-10ms. With HZ=1000 it's no problem. >> >> So if we have a 50HZ refresh rate, and a HZ rate of 250 or 300, it'll >> work fine then, right? I know that's actually some error in the timers, >> so it may be 2 or 3 ticks, not 1, but if we're running HZ at 5 or 6 >> times the frequency of video, presumably that'd still work fine? > > Yes, for PAL/NTSC, but it's nice to be forward looking... Well, looking forward, you'll have sub-HZ timers, so none of this will matter. Actually, looking at the above, 150 seems perfectly reasonable to me, but 300 seems to be close enough. I'll run some numbers on both. >From your above email, I'm more convinced than ever that lowering HZ is the right thing to do ... M. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
