forked from Minki/linux
5703d2f4a1
Fastsleep is one of the idle state which cpuidle subsystem currently uses on power8 machines. In this state L2 cache is brought down to a threshold voltage. Therefore when the core is in fastsleep, the communication between L2 and L3 needs to be fenced. But there is a bug in the current power8 chips surrounding this fencing. OPAL provides a workaround which precludes the possibility of hitting this bug. But running with this workaround applied causes checkstop if any correctable error in L2 cache directory is detected. Hence OPAL also provides a way to undo the workaround. In the existing implementation, workaround is applied by the last thread of the core entering fastsleep and undone by the first thread waking up. But this has a performance cost. These OPAL calls account for roughly 4000 cycles everytime the core has to enter or wakeup from fastsleep. This patch introduces a sysfs attribute (fastsleep_workaround_applyonce) to choose the behavior of this workaround. By default, fastsleep_workaround_applyonce = 0. In this case, workaround is applied/undone everytime the core enters/exits fastsleep. fastsleep_workaround_applyonce = 1. In this case the workaround is applied once on all the cores and never undone. This can be triggered by echo 1 > /sys/devices/system/cpu/fastsleep_workaround_applyonce For simplicity this attribute can be modified only once. Implying, once fastsleep_workaround_applyonce is changed to 1, it cannot be reverted to the default state. Signed-off-by: Shreyas B. Prabhu <shreyas@linux.vnet.ibm.com> Reviewed-by: Preeti U Murthy <preeti@linux.vnet.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> |
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| fsl_uli1575.c | ||
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