From: Ard Biesheuvel Date: Wed, 3 Feb 2021 11:36:18 +0000 (+0100) Subject: arm64: assembler: add cond_yield macro X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=d13c613f136c9090f3863c49b2306d57ab59feba;p=linux.git 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 Link: https://lore.kernel.org/r/20210203113626.220151-2-ardb@kernel.org Signed-off-by: Will Deacon --- diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h index bf125c5911168..27b1ea721c2df 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