On Thu, Feb 05, 2015 at 12:00:58PM +0100, Krzysztof Kozlowski wrote: > On czw, 2015-02-05 at 10:50 +0000, Russell King - ARM Linux wrote: > > On Thu, Feb 05, 2015 at 11:14:30AM +0100, Krzysztof Kozlowski wrote: > > > The complete() should not be used on offlined CPU. Rewrite the > > > wait-complete mechanism with wait_on_bit_timeout(). > > > > Yuck. > > > > I think that the IPI idea would be far better, and a much smaller patch. > > We can continue using the completions, but instead of running the > > completion on the dying CPU, the dying CPU triggers an IPI which does > > the completion on the requesting CPU. > > > > You're modifying arch/arm/kernel/smp.c, so you just hook it directly > > into the IPI mechanism without any registration required. > > > > We can also kill the second cache flush by the dying CPU - as we're > > not writing to memory anymore by calling complete() after the first > > cache flush, so this will probably make CPU hotplug fractionally faster > > too. > > > > (You'll get some fuzz with this patch as I have the NMI backtrace stuff > > in my kernel.) > > > > Something like this - only build tested so far (waiting for the compile > > to finish...): > > I am looking into IPI also. Maybe just smp_call_function_any() would be > enough?
I really don't like that idea. Let's keep it simple, and avoid calling code unnecessarily which could end up with RCU issues - and avoid the need for a second L1 cache flush. This does seem to work on iMX6 (if you ignore the lockdep splat caused by that frigging CMA lock - yes, that issue I reported earlier last year still exists and is still unsolved, which is really disgusting.) -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
