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4c73056e |
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16-Oct-2023 |
Mark Rutland <mark.rutland@arm.com> |
arm64: Avoid cpus_have_const_cap() for ARM64_HAS_WFXT In __delay() we use cpus_have_const_cap() to check for ARM64_HAS_WFXT, but this is not necessary and alternative_has_cap() would be preferable. For historical reasons, cpus_have_const_cap() is more complicated than it needs to be. Before cpucaps are finalized, it will perform a bitmap test of the system_cpucaps bitmap, and once cpucaps are finalized it will use an alternative branch. This used to be necessary to handle some race conditions in the window between cpucap detection and the subsequent patching of alternatives and static branches, where different branches could be out-of-sync with one another (or w.r.t. alternative sequences). Now that we use alternative branches instead of static branches, these are all patched atomically w.r.t. one another, and there are only a handful of cases that need special care in the window between cpucap detection and alternative patching. Due to the above, it would be nice to remove cpus_have_const_cap(), and migrate callers over to alternative_has_cap_*(), cpus_have_final_cap(), or cpus_have_cap() depending on when their requirements. This will remove redundant instructions and improve code generation, and will make it easier to determine how each callsite will behave before, during, and after alternative patching. The cpus_have_const_cap() check in __delay() is an optimization to use WFIT and WFET in preference to busy-polling the counter and/or using regular WFE and relying upon the architected timer event stream. It is not necessary to apply this optimization in the window between detecting the ARM64_HAS_WFXT cpucap and patching alternatives. This patch replaces the use of cpus_have_const_cap() with alternative_has_cap_unlikely(), which will avoid generating code to test the system_cpucaps bitmap and should be better for all subsequent calls at runtime. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Marc Zyngier <maz@kernel.org> Cc: Suzuki K Poulose <suzuki.poulose@arm.com> Cc: Will Deacon <will@kernel.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
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7b77452e |
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13-Oct-2017 |
Julien Thierry <julien.thierry.kdev@gmail.com> |
arm64: use WFE for long delays The current delay implementation uses the yield instruction, which is a hint that it is beneficial to schedule another thread. As this is a hint, it may be implemented as a NOP, causing all delays to be busy loops. This is the case for many existing CPUs. Taking advantage of the generic timer sending periodic events to all cores, we can use WFE during delays to reduce power consumption. This is beneficial only for delays longer than the period of the timer event stream. If timer event stream is not enabled, delays will behave as yield/busy loops. Signed-off-by: Julien Thierry <julien.thierry@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
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f27bb139 |
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05-Mar-2012 |
Marc Zyngier <maz@kernel.org> |
arm64: Miscellaneous library functions This patch adds udelay, memory and bit operations together with the ksyms exports. Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Tony Lindgren <tony@atomide.com> Acked-by: Nicolas Pitre <nico@linaro.org> Acked-by: Olof Johansson <olof@lixom.net> Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
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