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author | Vincent Guittot <vincent.guittot@linaro.org> | 2013-04-23 16:59:02 +0200 |
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committer | Ingo Molnar <mingo@kernel.org> | 2013-04-26 12:13:44 +0200 |
commit | 25f55d9d01ad7a7ad248fd5af1d22675ffd202c5 (patch) | |
tree | dc6ba0d1f4dc8119c7dd4d0844fa31a8ed60bf6f /init/do_mounts_rd.c | |
parent | e02e60c109ca70935bad1131976bdbf5160cf576 (diff) | |
download | linux-stable-25f55d9d01ad7a7ad248fd5af1d22675ffd202c5.tar.gz linux-stable-25f55d9d01ad7a7ad248fd5af1d22675ffd202c5.tar.bz2 linux-stable-25f55d9d01ad7a7ad248fd5af1d22675ffd202c5.zip |
sched: Fix init NOHZ_IDLE flag
On my SMP platform which is made of 5 cores in 2 clusters, I
have the nr_busy_cpu field of sched_group_power struct that is
not null when the platform is fully idle - which makes the
scheduler unhappy.
The root cause is:
During the boot sequence, some CPUs reach the idle loop and set
their NOHZ_IDLE flag while waiting for others CPUs to boot. But
the nr_busy_cpus field is initialized later with the assumption
that all CPUs are in the busy state whereas some CPUs have
already set their NOHZ_IDLE flag.
More generally, the NOHZ_IDLE flag must be initialized when new
sched_domains are created in order to ensure that NOHZ_IDLE and
nr_busy_cpus are aligned.
This condition can be ensured by adding a synchronize_rcu()
between the destruction of old sched_domains and the creation of
new ones so the NOHZ_IDLE flag will not be updated with old
sched_domain once it has been initialized. But this solution
introduces a additionnal latency in the rebuild sequence that is
called during cpu hotplug.
As suggested by Frederic Weisbecker, another solution is to have
the same rcu lifecycle for both NOHZ_IDLE and sched_domain
struct. A new nohz_idle field is added to sched_domain so both
status and sched_domain will share the same RCU lifecycle and
will be always synchronized. In addition, there is no more need
to protect nohz_idle against concurrent access as it is only
modified by 2 exclusive functions called by local cpu.
This solution has been prefered to the creation of a new struct
with an extra pointer indirection for sched_domain.
The synchronization is done at the cost of :
- An additional indirection and a rcu_dereference for accessing nohz_idle.
- We use only the nohz_idle field of the top sched_domain.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: linaro-kernel@lists.linaro.org
Cc: peterz@infradead.org
Cc: fweisbec@gmail.com
Cc: pjt@google.com
Cc: rostedt@goodmis.org
Cc: efault@gmx.de
Link: http://lkml.kernel.org/r/1366729142-14662-1-git-send-email-vincent.guittot@linaro.org
[ Fixed !NO_HZ build bug. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'init/do_mounts_rd.c')
0 files changed, 0 insertions, 0 deletions