On Wed, 2013-07-17 at 18:44 +0200, Frederic Weisbecker wrote:
> The code is ready to do so in the context tracking subsystem, now
"do so"? Do what?
> we just need to pass our cpu range selection to it from the
Pass cpu range selection to what?
Pronouns are evil in technical documentation.
> full dynticks subsystem.
>
> This way we can spare the overhead of RCU user extended quiescent
> state and vtime maintainance on these CPUs. Just keep in mind the
> context tracking itself is still necessary everywhere.
>
> Signed-off-by: Frederic Weisbecker <fweis...@gmail.com>
> Cc: Steven Rostedt <rost...@goodmis.org>
> Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> Cc: Ingo Molnar <mi...@kernel.org>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: Borislav Petkov <b...@alien8.de>
> Cc: Li Zhong <zh...@linux.vnet.ibm.com>
> Cc: Mike Galbraith <efa...@gmx.de>
> Cc: Kevin Hilman <khil...@linaro.org>
> ---
> include/linux/context_tracking.h | 2 ++
> init/Kconfig | 2 +-
> kernel/context_tracking.c | 5 +++++
> kernel/time/Kconfig | 1 -
> kernel/time/tick-sched.c | 6 ++++++
> 5 files changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/context_tracking.h
> b/include/linux/context_tracking.h
> index 12045ce..2c2b73aa 100644
> --- a/include/linux/context_tracking.h
> +++ b/include/linux/context_tracking.h
> @@ -34,6 +34,8 @@ static inline bool context_tracking_active(void)
> return __this_cpu_read(context_tracking.active);
> }
>
> +extern void context_tracking_cpu_set(int cpu);
> +
> extern void user_enter(void);
> extern void user_exit(void);
>
> diff --git a/init/Kconfig b/init/Kconfig
> index 247084b..914da3f 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -527,7 +527,7 @@ config RCU_USER_QS
> config CONTEXT_TRACKING_FORCE
> bool "Force context tracking"
> depends on CONTEXT_TRACKING
> - default CONTEXT_TRACKING
> + default y if !NO_HZ_FULL
Why the if !NO_HZ_FULL?
That selects this anyway. Oh wait, you changed this.
> help
> Probe on user/kernel boundaries by default in order to
> test the features that rely on it such as userspace RCU extended
> diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
> index 7b095de..72bcb25 100644
> --- a/kernel/context_tracking.c
> +++ b/kernel/context_tracking.c
> @@ -26,6 +26,11 @@ DEFINE_PER_CPU(struct context_tracking, context_tracking)
> = {
> #endif
> };
>
> +void context_tracking_cpu_set(int cpu)
> +{
> + per_cpu(context_tracking.active, cpu) = true;
> +}
> +
> /**
> * user_enter - Inform the context tracking that the CPU is going to
> * enter userspace mode.
> diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
> index 70f27e8..747bbc7 100644
> --- a/kernel/time/Kconfig
> +++ b/kernel/time/Kconfig
> @@ -105,7 +105,6 @@ config NO_HZ_FULL
> select RCU_USER_QS
> select RCU_NOCB_CPU
> select VIRT_CPU_ACCOUNTING_GEN
> - select CONTEXT_TRACKING_FORCE
OK, I'm confused.
-- Steve
> select IRQ_WORK
> help
> Adaptively try to shutdown the tick whenever possible, even when
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index 088c411..062759e 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -23,6 +23,7 @@
> #include <linux/irq_work.h>
> #include <linux/posix-timers.h>
> #include <linux/perf_event.h>
> +#include <linux/context_tracking.h>
>
> #include <asm/irq_regs.h>
>
> @@ -344,11 +345,16 @@ static int tick_nohz_init_all(void)
>
> void __init tick_nohz_init(void)
> {
> + int cpu;
> +
> if (!have_nohz_full_mask) {
> if (tick_nohz_init_all() < 0)
> return;
> }
>
> + for_each_cpu(cpu, nohz_full_mask)
> + context_tracking_cpu_set(cpu);
> +
> cpu_notifier(tick_nohz_cpu_down_callback, 0);
> cpulist_scnprintf(nohz_full_buf, sizeof(nohz_full_buf), nohz_full_mask);
> pr_info("NO_HZ: Full dynticks CPUs: %s.\n", nohz_full_buf);
--
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