On Mon, Nov 16, 2015 at 11:10:55AM -0800, Andy Lutomirski wrote: > On Nov 13, 2015 7:26 AM, "Frederic Weisbecker" <fweis...@gmail.com> wrote: > > > > On Thu, Nov 12, 2015 at 12:59:04PM -0800, Andy Lutomirski wrote: > > > On CONFIG_CONTEXT_TRACKING kernels that have context tracking > > > disabled at runtime (which includes most distro kernels), we still > > > have the overhead of a call to enter_from_user_mode in interrupt and > > > exception entries. > > > > > > If jump labels are available, this uses the jump label > > > infrastructure to skip the call. > > > > Looks good. But why are we still calling context tracking code on IRQs at > > all? > > Same reasons as before: > > 1. This way the IRQ exit path is almost completely shared with all the > other exit paths.
I'm all for consolidation in general. Unless it brings bad middle states. If I knew before that I would have to argue endlessly in order to protest against these context tracking changes, I would have NACK'ed the x86 consolidation rework in the state it was while it got merged. > > 2. It combines the checks for which context we were in with what CPL > we entered from. > > Part 2 should be complete across the whole x86 kernel soon once the > 64-bit syscall code gets fixed up. > > We should get rid of the duplication in the irq entry hooks. Want to > help with that? Which one? The duplication against irq_enter() and irq_exit()? I think that irq_exit() should be moved to the IRQ very end and perform the final signal/schedule/preempt_schedule_irq() loop. But it requires a bit of rework on all archs in order to do that. This could be done iteratively though. > Presumably we should do the massive remote polling speedup to the nohz code, Hmm, I don't get what you mean here. > and we should also teach enter_from_user_mode to transition directly to IRQ > state as > appropriate. Then irq_enter can be much faster. I don't get what you mean here either. You mean calling irq_enter() from enter_from_user_mode()? -- 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/
