* Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> [081207 09:06]: > On Sun, Dec 07, 2008 at 08:55:54AM -0600, Woodruff, Richard wrote: > > Yes, NOHZ is _poor_ today in respect to needless reprogramming. Code can > > be improved. I have sent Thomas a patch for the same which is in the MM > > tree for a while now. > > When I discussed this problem with Thomas, his reaction was rather > negative due to there being conflicting requirements between this and > ia64. And quite frankly I think that the OMAP behaviour is utter > madness - taking as long as it does to update the timer registers > means that no matter what you do, you _will_ be paying a penalty > for that hardware. Well still the timer code should be optimized for slower systems. The timer should not be reprogrammed during every device interrupt if the change is less than a jiffy. And going through the timer lists is not always needed, so Richard's patch tries to optimize that [1]. > Let's hope that later OMAP designs sanitise the timer hardware so > it doesn't take stupid amounts of time to write to the registers, > posted mode or not. Yeah. Richard has some profiling data showing you how much time is spent doing that, maybe post that again for reference? It's very interesting data. Tony [1] http://www.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.28-rc2/2.6.28-rc2-mm1/broken-out/tick-schedc-suppress-needless-timer-reprogramming.patch -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
