On Fri, 17 Oct 2008, Mathieu Desnoyers wrote: > > Hrm, on such systems > - *large* amount of cpus > - no synchronized TSCs > > What would be the best approach to order events ? My strong opinion has been - for a longish while now, and independently of any timestamping code - that we should be seriously looking at basically doing essentially a "ntp" inside the kernel to give up the whole idiotic notion of "synchronized TSCs". Yes, TSC's are often synchronized, but even when they are, we might as well _think_ of them as not being so. In other words, instead of expecting internal clocks to be synchronized, just make the clock be a clock network of independent TSC domains. The domains could in theory be per-package (assuming TSC is synchronized at that level), but even if we _could_ do that, we'd probably still be better off by simply always doing it per-core. If only because then the reading would be per-core. I think it's a mistake for us to maintain a single clock for gettimeofday() (well, "getnstimeofday" and the whole "clocksource_read()" crud to be technically correct). And sure, I bet clocksource_read() can do various per-CPU things and try to do that, but it's complex and pretty generic code, and as far as I know none of the clocksources have even tried. The TSC clocksource read certainly does not (it just does a very similar horrible "at least don't go backwards" crud that the LTTng patch suggested). So I think we should make "xtime" be a per-CPU thing, and add support for per-CPU clocksources. And screw that insane "mark_tsc_unstable()" thing. And if we did it well, we migth be able to get good timestamps that way too. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
