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On Tue, 2007-08-28 at 08:23 +0300, Al Boldi wrote: > Linus Torvalds wrote:> > On Tue, 28 Aug 2007, Al Boldi wrote:> > > No need for framebuffer. All you need is X using the X.org vesa-driver. > > > Then start gears like this:> > >> > > # gears & gears & gears & > > > > > > Then lay them out side by side to see the periodic stallings for ~10sec.> >> > I don't think this is a good test.> >> > Why?> >> > If you're not using direct rendering, what you have is the X server doing > > all the rendering, which in turn means that what you are testing is quite > > possibly not so much about the *kernel* scheduling, but about *X-server* > > scheduling!> >> > I'm sure the kernel scheduler has an impact, but what's more likely to be > > going on is that you're seeing effects that are indirect, and not > > necessarily at all even "good".> >> > For example, if the X server is the scheduling point, it's entirely > > possible that it ends up showing effects that are more due to the queueing > > of the X command stream than due to the scheduler - and that those > > stalls are simply due to *that*.> >> > One thing to try is to run the X connection in synchronous mode, which > > minimizes queueing issues. I don't know if gears has a flag to turn on > > synchronous X messaging, though. Many X programs take the "[+-]sync" flag > > to turn on synchronous mode, iirc.> > I like your analysis, but how do you explain that these stalls vanish when > __update_curr is disabled? When you disable __update_curr(), you're utterly destroying the scheduler. There may well be a scheduler connection, but disabling __update_curr() doesn't tell you anything meaningful. Basically, you're letting all tasks run uninterrupted for just as long as they please (which is why busy loops lock your box solid as a rock). I'd suggest gathering some sched_debug stats or something... shoot, _anything_ but what you did :) -Mike - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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