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arm64: assembler: Update comment above cond_yield_neon() macro

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Since commit 7faa313f05 ("arm64: preempt: Fix big-endian when checking
preempt count in assembly") both the preempt count and the 'need_resched'
flag are checked as part of a single 64-bit load in cond_yield_neon(),
so update the stale comment to reflect reality.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Dave Martin <Dave.Martin@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Hillf Danton <hdanton@sina.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Hillf Danton 2019-05-14 16:34:19 +08:00 committed by Will Deacon
parent 14ae42a6f0
commit 0e4add4ae7
1 changed files with 5 additions and 6 deletions
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11
arch/arm64/include/asm/assembler.h
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@ -718,12 +718,11 @@ USER(\label, ic ivau, \tmp2) // invalidate I line PoU
* the output section, any use of such directives is undefined.
*
* The yield itself consists of the following:
* - Check whether the preempt count is exactly 1, in which case disabling
* preemption once will make the task preemptible. If this is not the case,
* yielding is pointless.
* - Check whether TIF_NEED_RESCHED is set, and if so, disable and re-enable
* kernel mode NEON (which will trigger a reschedule), and branch to the
* yield fixup code.
* - Check whether the preempt count is exactly 1 and a reschedule is also
* needed. If so, calling of preempt_enable() in kernel_neon_end() will
* trigger a reschedule. If it is not the case, yielding is pointless.
* - Disable and re-enable kernel mode NEON, and branch to the yield fixup
* code.
*
* This macro sequence may clobber all CPU state that is not guaranteed by the
* AAPCS to be preserved across an ordinary function call.