iv/linux
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

arm64: fpsimd: Bring cond_yield asm macro in line with new rules

Browse Source 
We no longer disable softirqs or preemption when doing kernel mode SIMD,
and so for fully preemptible kernels, there is no longer a need to do any
explicit yielding (and for non-preemptible kernels, yielding is not
needed either).

That leaves voluntary preemption, where only explicit yield calls may
result in a reschedule. To retain the existing behavior for such a
configuration, we should take the new situation into account, where the
preempt count will be zero rather than one, and yielding to pending
softirqs is unnecessary.

Fixes: aefbab8e77eb ("arm64: fpsimd: Preserve/restore kernel mode NEON at context switch")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20240111112447.577640-2-ardb+git@google.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Ard Biesheuvel 2024-01-11 12:24:48 +01:00 committed by Will Deacon
parent 8c5a19cb17
commit 3931261ecf
2 changed files with 9 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
arch/arm64/include/asm/assembler.h
View File

@ -760,32 +760,25 @@ alternative_endif
.endm
/*
* Check whether preempt/bh-disabled asm code should yield as soon as
* it is able. This is the case if we are currently running in task
* context, and either a softirq is pending, or the TIF_NEED_RESCHED
* flag is set and re-enabling preemption a single time would result in
* a preempt count of zero. (Note that the TIF_NEED_RESCHED flag is
* stored negated in the top word of the thread_info::preempt_count
* Check whether asm code should yield as soon as it is able. This is
* the case if we are currently running in task context, and the
* TIF_NEED_RESCHED flag is set. (Note that the TIF_NEED_RESCHED flag
* is stored negated in the top word of the thread_info::preempt_count
* field)
*/
.macro cond_yield, lbl:req, tmp:req, tmp2:req
.macro cond_yield, lbl:req, tmp:req, tmp2
#ifdef CONFIG_PREEMPT_VOLUNTARY
get_current_task \tmp
ldr \tmp, [\tmp, #TSK_TI_PREEMPT]
/*
* If we are serving a softirq, there is no point in yielding: the
* softirq will not be preempted no matter what we do, so we should
* run to completion as quickly as we can.
* run to completion as quickly as we can. The preempt_count field will
* have BIT(SOFTIRQ_SHIFT) set in this case, so the zero check will
* catch this case too.
*/
tbnz \tmp, #SOFTIRQ_SHIFT, .Lnoyield_\@
#ifdef CONFIG_PREEMPTION
sub \tmp, \tmp, #PREEMPT_DISABLE_OFFSET
cbz \tmp, \lbl
#endif
adr_l \tmp, irq_stat + IRQ_CPUSTAT_SOFTIRQ_PENDING
get_this_cpu_offset \tmp2
ldr w\tmp, [\tmp, \tmp2]
cbnz w\tmp, \lbl // yield on pending softirq in task context
.Lnoyield_\@:
.endm
/*

2
arch/arm64/kernel/asm-offsets.c
View File

@ -117,8 +117,6 @@ int main(void)
DEFINE(DMA_FROM_DEVICE, DMA_FROM_DEVICE);
BLANK();
DEFINE(PREEMPT_DISABLE_OFFSET, PREEMPT_DISABLE_OFFSET);
DEFINE(SOFTIRQ_SHIFT, SOFTIRQ_SHIFT);
DEFINE(IRQ_CPUSTAT_SOFTIRQ_PENDING, offsetof(irq_cpustat_t, __softirq_pending));
BLANK();
DEFINE(CPU_BOOT_TASK, offsetof(struct secondary_data, task));
BLANK();