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19209bbb86
The checks that exist in mwait_usable() for "idle=" kernel parameters are insufficient. As a result, mwait_usable() can return 1 even if "idle=nomwait" or "idle=poll" or "idle=halt" parameters are passed. Of these cases, incorrect handling of idle=nomwait is a universal problem since mwait can get used for usual CPU idling. However the rest of the cases are problematic only during CPU Hotplug (offline) because, in the CPU offline path, the function mwait_play_dead() is called, which might result in mwait being used in the offline CPUs, if mwait_usable() happens to return 1. Fix these issues by checking for the boot time "idle=" kernel parameter properly in mwait_usable(). The first issue (usual cpu idling) is demonstrated below: Before applying the patch (dmesg snippet): [ 0.000000] Command line: [...] idle=nomwait [ 0.000000] Kernel command line: [...] idle=nomwait [ 0.000000] RCU dyntick-idle grace-period acceleration is enabled. [ 0.140606] using mwait in idle threads. <======= mwait being used [ 4.303986] cpuidle: using governor ladder [ 4.308232] cpuidle: using governor menu After applying the patch: [ 0.000000] Command line: [...] idle=nomwait [ 0.000000] Kernel command line: [...] idle=nomwait [ 0.000000] RCU dyntick-idle grace-period acceleration is enabled. [ 4.264100] cpuidle: using governor ladder [ 4.268342] cpuidle: using governor menu Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Acked-by: Deepthi Dharwar <deepthi@linux.vnet.ibm.com> Acked-by: Thomas Gleixner <tglx@linutronix.de> Cc: venki@google.com Cc: suresh.b.siddha@intel.com Cc: Borislav Petkov <bp@amd64.org> Cc: lenb@kernel.org Cc: Rafael J. Wysocki <rjw@sisk.pl> Link: http://lkml.kernel.org/r/4F9E37B8.30001@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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