diff options
| author | Ard Biesheuvel <ardb@kernel.org> | 2021-02-03 12:36:18 +0100 |
|---|---|---|
| committer | Will Deacon <will@kernel.org> | 2021-02-03 20:48:02 +0000 |
| commit | d13c613f136c9090f3863c49b2306d57ab59feba (patch) | |
| tree | 1460b7bd70176eefcf74869c55d31e15908e4535 /arch/arm64/include | |
| parent | 5c8fe583cce542aa0b84adc939ce85293de36e5e (diff) | |
arm64: assembler: add cond_yield macro
Add a macro cond_yield that branches to a specified label when called if
the TIF_NEED_RESCHED flag is set and decreasing the preempt count would
make the task preemptible again, resulting in a schedule to occur. This
can be used by kernel mode SIMD code that keeps a lot of state in SIMD
registers, which would make chunking the input in order to perform the
cond_resched() check from C code disproportionately costly.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20210203113626.220151-2-ardb@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'arch/arm64/include')
| -rw-r--r-- | arch/arm64/include/asm/assembler.h | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h index bf125c591116..27b1ea721c2d 100644 --- a/arch/arm64/include/asm/assembler.h +++ b/arch/arm64/include/asm/assembler.h @@ -745,6 +745,22 @@ USER(\label, ic ivau, \tmp2) // invalidate I line PoU .Lyield_out_\@ : .endm + /* + * Check whether preempt-disabled code should yield as soon as it + * is able. This is the case if re-enabling preemption a single + * time results in a preempt count of zero, and the TIF_NEED_RESCHED + * flag is set. (Note that the latter is stored negated in the + * top word of the thread_info::preempt_count field) + */ + .macro cond_yield, lbl:req, tmp:req +#ifdef CONFIG_PREEMPTION + get_current_task \tmp + ldr \tmp, [\tmp, #TSK_TI_PREEMPT] + sub \tmp, \tmp, #PREEMPT_DISABLE_OFFSET + cbz \tmp, \lbl +#endif + .endm + /* * This macro emits a program property note section identifying * architecture features which require special handling, mainly for |