Messages in this thread | | | Date | Wed, 21 Mar 2018 15:22:27 +0000 | From | Dave Martin <> | Subject | Re: [PATCH v4 21/22] arm64: Delay enabling hardware DBM feature |
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On Tue, Mar 13, 2018 at 11:51:19AM +0000, Suzuki K Poulose wrote: > We enable hardware DBM bit in a capable CPU, very early in the > boot via __cpu_setup. This doesn't give us a flexibility of > optionally disable the feature, as the clearing the bit > is a bit costly as the TLB can cache the settings. Instead, > we delay enabling the feature until the CPU is brought up > into the kernel. We use the feature capability mechanism > to handle it. > > The hardware DBM is a non-conflicting feature. i.e, the kernel > can safely run with a mix of CPUs with some using the feature > and the others don't. So, it is safe for a late CPU to have > this capability and enable it, even if the active CPUs don't. > > To get this handled properly by the infrastructure, we > unconditionally set the capability and only enable it > on CPUs which really have the feature. Also, we print the > feature detection from the "matches" call back to make sure > we don't mislead the user when none of the CPUs could use the > feature. > > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Dave Martin <dave.martin@arm.com> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
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Reviewed-by: Dave Martin <Dave.Martin@arm.com>
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