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    SubjectRe: [PATCH 08/33] nohz: Assign timekeeping duty to a non-full-nohz CPU
    From
    2013/2/15 Borislav Petkov <bp@alien8.de>:
    > On Tue, Jan 08, 2013 at 03:08:08AM +0100, Frederic Weisbecker wrote:
    >> This way the full nohz CPUs can safely run with the tick
    >> stopped with a guarantee that somebody else is taking
    >> care of the jiffies and gtod progression.
    >>
    >> NOTE: this doesn't handle CPU hotplug. Also we could use something
    >> more elaborated wrt. powersaving if we have more than one non full-nohz
    >> CPU running. But let's use this KISS solution for now.
    >>
    >> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
    >> Cc: Alessio Igor Bogani <abogani@kernel.org>
    >> Cc: Andrew Morton <akpm@linux-foundation.org>
    >> Cc: Chris Metcalf <cmetcalf@tilera.com>
    >> Cc: Christoph Lameter <cl@linux.com>
    >> Cc: Geoff Levand <geoff@infradead.org>
    >> Cc: Gilad Ben Yossef <gilad@benyossef.com>
    >> Cc: Hakan Akkan <hakanakkan@gmail.com>
    >> Cc: Ingo Molnar <mingo@kernel.org>
    >> Cc: Li Zhong <zhong@linux.vnet.ibm.com>
    >> Cc: Namhyung Kim <namhyung.kim@lge.com>
    >> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    >> Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
    >> Cc: Peter Zijlstra <peterz@infradead.org>
    >> Cc: Steven Rostedt <rostedt@goodmis.org>
    >> Cc: Thomas Gleixner <tglx@linutronix.de>
    >> [fix have_nohz_full_mask offcase]
    >> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    >> ---
    >> kernel/time/tick-broadcast.c | 3 ++-
    >> kernel/time/tick-common.c | 5 ++++-
    >> kernel/time/tick-sched.c | 9 ++++++++-
    >> 3 files changed, 14 insertions(+), 3 deletions(-)
    >>
    >> diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
    >> index f113755..596c547 100644
    >> --- a/kernel/time/tick-broadcast.c
    >> +++ b/kernel/time/tick-broadcast.c
    >> @@ -537,7 +537,8 @@ void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
    >> bc->event_handler = tick_handle_oneshot_broadcast;
    >>
    >> /* Take the do_timer update */
    >> - tick_do_timer_cpu = cpu;
    >> + if (!tick_nohz_full_cpu(cpu))
    >> + tick_do_timer_cpu = cpu;
    >>
    >> /*
    >> * We must be careful here. There might be other CPUs
    >> diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
    >> index b1600a6..83f2bd9 100644
    >> --- a/kernel/time/tick-common.c
    >> +++ b/kernel/time/tick-common.c
    >> @@ -163,7 +163,10 @@ static void tick_setup_device(struct tick_device *td,
    >> * this cpu:
    >> */
    >> if (tick_do_timer_cpu == TICK_DO_TIMER_BOOT) {
    >> - tick_do_timer_cpu = cpu;
    >> + if (!tick_nohz_full_cpu(cpu))
    >> + tick_do_timer_cpu = cpu;
    >> + else
    >> + tick_do_timer_cpu = TICK_DO_TIMER_NONE;
    >> tick_next_period = ktime_get();
    >> tick_period = ktime_set(0, NSEC_PER_SEC / HZ);
    >> }
    >> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
    >> index 494a2aa..b75e302 100644
    >> --- a/kernel/time/tick-sched.c
    >> +++ b/kernel/time/tick-sched.c
    >> @@ -112,7 +112,8 @@ static void tick_sched_do_timer(ktime_t now)
    >> * this duty, then the jiffies update is still serialized by
    >> * jiffies_lock.
    >> */
    >> - if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE))
    >> + if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)
    >> + && !tick_nohz_full_cpu(cpu))
    >> tick_do_timer_cpu = cpu;
    >> #endif
    >>
    >> @@ -163,6 +164,8 @@ static int __init tick_nohz_full_setup(char *str)
    >> return 1;
    >> }
    >> __setup("full_nohz=", tick_nohz_full_setup);
    >> +#else
    >> +#define have_full_nohz_mask (0)
    >> #endif
    >
    > Looks like this hunk should be part of the previous patch, no?

    Ah probably yeah :)

    > Oui, oui monsieur! :-)

    :)


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