| Message ID | 1509728692-10460-13-git-send-email-cmetcalf@mellanox.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Chris, On Fri, Nov 03, 2017 at 01:04:51PM -0400, Chris Metcalf wrote: > diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c > index fd4b7f684bd0..61ea7f907c56 100644 > --- a/drivers/clocksource/arm_arch_timer.c > +++ b/drivers/clocksource/arm_arch_timer.c > @@ -722,6 +722,8 @@ static void __arch_timer_setup(unsigned type, > } > } > > + clk->set_state_oneshot_stopped = clk->set_state_shutdown; AFAICT, we've set up this callback since commit: cf8c5009ee37d25c ("clockevents/drivers/arm_arch_timer: Implement ->set_state_oneshot_stopped()") ... so I don't beleive this is necessary, and I think this change can be dropped. Thanks, Mark.
On 11/3/2017 1:18 PM, Mark Rutland wrote: > Hi Chris, > > On Fri, Nov 03, 2017 at 01:04:51PM -0400, Chris Metcalf wrote: >> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c >> index fd4b7f684bd0..61ea7f907c56 100644 >> --- a/drivers/clocksource/arm_arch_timer.c >> +++ b/drivers/clocksource/arm_arch_timer.c >> @@ -722,6 +722,8 @@ static void __arch_timer_setup(unsigned type, >> } >> } >> >> + clk->set_state_oneshot_stopped = clk->set_state_shutdown; > AFAICT, we've set up this callback since commit: > > cf8c5009ee37d25c ("clockevents/drivers/arm_arch_timer: Implement ->set_state_oneshot_stopped()") > > ... so I don't beleive this is necessary, and I think this change can be > dropped. Thanks, I will drop it. I missed the semantic merge conflict there. I extracted the arch/tile specific part of the change and just pushed it through the tile tree.
diff --git a/arch/tile/kernel/time.c b/arch/tile/kernel/time.c index f74f10d827fa..afca6fe496c8 100644 --- a/arch/tile/kernel/time.c +++ b/arch/tile/kernel/time.c @@ -163,6 +163,7 @@ static DEFINE_PER_CPU(struct clock_event_device, tile_timer) = { .set_next_event = tile_timer_set_next_event, .set_state_shutdown = tile_timer_shutdown, .set_state_oneshot = tile_timer_shutdown, + .set_state_oneshot_stopped = tile_timer_shutdown, .tick_resume = tile_timer_shutdown, }; diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c index fd4b7f684bd0..61ea7f907c56 100644 --- a/drivers/clocksource/arm_arch_timer.c +++ b/drivers/clocksource/arm_arch_timer.c @@ -722,6 +722,8 @@ static void __arch_timer_setup(unsigned type, } } + clk->set_state_oneshot_stopped = clk->set_state_shutdown; + clk->set_state_shutdown(clk); clockevents_config_and_register(clk, arch_timer_rate, 0xf, 0x7fffffff);
When the schedule tick is disabled in tick_nohz_stop_sched_tick(), we call hrtimer_cancel(), which eventually calls down into __remove_hrtimer() and thus into hrtimer_force_reprogram(). That function's call to tick_program_event() detects that we are trying to set the expiration to KTIME_MAX and calls clockevents_switch_state() to set the state to ONESHOT_STOPPED, and returns. See commit 8fff52fd5093 ("clockevents: Introduce CLOCK_EVT_STATE_ONESHOT_STOPPED state") for more background. However, by default the internal __clockevents_switch_state() code doesn't have a "set_state_oneshot_stopped" function pointer for the arm_arch_timer or tile clock_event_device structures, so that code returns -ENOSYS, and we end up not setting the state, and more importantly, we don't actually turn off the hardware timer. As a result, the timer tick we were waiting for before is still queued, and fires shortly afterwards, only to discover there was nothing for it to do, at which point it quiesces. The fix is to provide that function pointer field, and like the other function pointers, have it just turn off the timer interrupt. Any call to set a new timer interval will properly re-enable it. This fix avoids a small performance hiccup for regular applications, but for TASK_ISOLATION code, it fixes a potentially serious kernel timer interruption to the time-sensitive application. Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com> Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org> --- arch/tile/kernel/time.c | 1 + drivers/clocksource/arm_arch_timer.c | 2 ++ 2 files changed, 3 insertions(+)