On Mon, Jul 13, 2015 at 5:57 PM, Peter Zijlstra <pet...@infradead.org> wrote: > On Fri, Jul 10, 2015 at 12:26:21PM -0500, Christoph Lameter wrote: >> On Thu, 9 Jul 2015, Chris Mason wrote: >> >> > I think the topic is really interesting and we'll be able to get numbers >> > from production workloads to help justify and compare different >> > approaches. >> >> Ok that would be important. I also think that the approach may be used >> in kernel to reduce the overhead of CONFIG_PREEMPT and also to implement >> fast versions of this_cpu_ops for non x86 architectures and maybe even > > There is nothing stopping people from trying this in-kernel, in fact > that would be lots easier as we do not have to commit to any one > specific ABI for that.
It also provides us a nicer way to fight with NMI and to modify a slight-biger-struct irq-safely if we have it in-kenrel. > > Also, I don't think we need a schedule check for the in-kernel usage, > pure interrupt should be good enough, nobody should (want to) call > schedule() while inside such a critical section, which leaves us with > involuntary preemption, and those are purely interrupt driven. > > Now the 'problem' is finding these special regions fast, the easy > solution is the same as the one proposed for userspace, one big section. > That way the interrupt only has to check if the IP is inside this > section which is minimal effort. > > The down side is that all percpu ops would then end up being full > function calls. Which on some archs is indeed faster than disabling > interrupts, but not by much I'm afraid. > >> optimize the x86 variants if interrupts also can detect critical sections >> and restart at defined points. > > I really don't see how we can beat %GS prefixes with any such scheme. > -- > 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/ -- 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/
