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authorDaniel Lezcano <daniel.lezcano@linaro.org>2014-09-04 19:32:09 +0400
committerIngo Molnar <mingo@kernel.org>2014-09-24 16:46:58 +0400
commit442bf3aaf55a91ebfec71da46a4ee10a3c905bcc (patch)
tree803aaeb75bbae35618fa9e7355fe97ffa3c12b21 /drivers
parent91ec6778ec4f963fcb2c2793610919b572f633b0 (diff)
downloadlinux-442bf3aaf55a91ebfec71da46a4ee10a3c905bcc.tar.xz
sched: Let the scheduler see CPU idle states
When the cpu enters idle, it stores the cpuidle state pointer in its struct rq instance which in turn could be used to make a better decision when balancing tasks. As soon as the cpu exits its idle state, the struct rq reference is cleared. There are a couple of situations where the idle state pointer could be changed while it is being consulted: 1. For x86/acpi with dynamic c-states, when a laptop switches from battery to AC that could result on removing the deeper idle state. The acpi driver triggers: 'acpi_processor_cst_has_changed' 'cpuidle_pause_and_lock' 'cpuidle_uninstall_idle_handler' 'kick_all_cpus_sync'. All cpus will exit their idle state and the pointed object will be set to NULL. 2. The cpuidle driver is unloaded. Logically that could happen but not in practice because the drivers are always compiled in and 95% of them are not coded to unregister themselves. In any case, the unloading code must call 'cpuidle_unregister_device', that calls 'cpuidle_pause_and_lock' leading to 'kick_all_cpus_sync' as mentioned above. A race can happen if we use the pointer and then one of these two scenarios occurs at the same moment. In order to be safe, the idle state pointer stored in the rq must be used inside a rcu_read_lock section where we are protected with the 'rcu_barrier' in the 'cpuidle_uninstall_idle_handler' function. The idle_get_state() and idle_put_state() accessors should be used to that effect. Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org> Signed-off-by: Nicolas Pitre <nico@linaro.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net> Cc: linux-pm@vger.kernel.org Cc: linaro-kernel@lists.linaro.org Cc: Daniel Lezcano <daniel.lezcano@linaro.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/n/tip-@git.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/cpuidle/cpuidle.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index d31e04ca8703..125150dc6e81 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -225,6 +225,12 @@ void cpuidle_uninstall_idle_handler(void)
initialized = 0;
wake_up_all_idle_cpus();
}
+
+ /*
+ * Make sure external observers (such as the scheduler)
+ * are done looking at pointed idle states.
+ */
+ synchronize_rcu();
}
/**