2024-04-20 05:16:52

by Dawei Li

Subject: [PATCH v2 2/7] sparc/irq: Remove on-stack cpumask var

In general it's preferable to avoid placing cpumasks on the stack, as
for large values of NR_CPUS these can consume significant amounts of
stack space and make stack overflows more likely.

- Both 2 arguments of cpumask_equal() is constant and free of change, no
need to allocate extra cpumask variables.

- Merge cpumask_and(), cpumask_first() and cpumask_empty() into
cpumask_first_and().

Signed-off-by: Dawei Li <[email protected]>
---
arch/sparc/kernel/irq_64.c | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/arch/sparc/kernel/irq_64.c b/arch/sparc/kernel/irq_64.c
index 5280e325d4d6..01ee800efde3 100644
--- a/arch/sparc/kernel/irq_64.c
+++ b/arch/sparc/kernel/irq_64.c
@@ -349,17 +349,13 @@ static unsigned int sun4u_compute_tid(unsigned long imap, unsigned long cpuid)
#ifdef CONFIG_SMP
static int irq_choose_cpu(unsigned int irq, const struct cpumask *affinity)
{
- cpumask_t mask;
int cpuid;

- cpumask_copy(&mask, affinity);
- if (cpumask_equal(&mask, cpu_online_mask)) {
+ if (cpumask_equal(affinity, cpu_online_mask)) {
cpuid = map_to_cpu(irq);
} else {
- cpumask_t tmp;
-
- cpumask_and(&tmp, cpu_online_mask, &mask);
- cpuid = cpumask_empty(&tmp) ? map_to_cpu(irq) : cpumask_first(&tmp);
+ cpuid = cpumask_first_and(affinity, cpu_online_mask);
+ cpuid = cpuid < nr_cpu_ids ? cpuid : map_to_cpu(irq);
}

return cpuid;
--
2.27.0

2024-04-20 08:24:08

by Sam Ravnborg

Subject: Re: [PATCH v2 2/7] sparc/irq: Remove on-stack cpumask var

On Sat, Apr 20, 2024 at 01:15:42PM +0800, Dawei Li wrote:
> In general it's preferable to avoid placing cpumasks on the stack, as
> for large values of NR_CPUS these can consume significant amounts of
> stack space and make stack overflows more likely.
>
> - Both 2 arguments of cpumask_equal() is constant and free of change, no
> need to allocate extra cpumask variables.
>
> - Merge cpumask_and(), cpumask_first() and cpumask_empty() into
> cpumask_first_and().
>
> Signed-off-by: Dawei Li <[email protected]>
Reviewed-by: Sam Ravnborg <[email protected]>
> ---
> arch/sparc/kernel/irq_64.c | 10 +++-------
> 1 file changed, 3 insertions(+), 7 deletions(-)
>
> diff --git a/arch/sparc/kernel/irq_64.c b/arch/sparc/kernel/irq_64.c
> index 5280e325d4d6..01ee800efde3 100644
> --- a/arch/sparc/kernel/irq_64.c
> +++ b/arch/sparc/kernel/irq_64.c
> @@ -349,17 +349,13 @@ static unsigned int sun4u_compute_tid(unsigned long imap, unsigned long cpuid)
> #ifdef CONFIG_SMP
> static int irq_choose_cpu(unsigned int irq, const struct cpumask *affinity)
> {
> - cpumask_t mask;
> int cpuid;
>
> - cpumask_copy(&mask, affinity);
> - if (cpumask_equal(&mask, cpu_online_mask)) {
> + if (cpumask_equal(affinity, cpu_online_mask)) {
> cpuid = map_to_cpu(irq);
> } else {
> - cpumask_t tmp;
> -
> - cpumask_and(&tmp, cpu_online_mask, &mask);
> - cpuid = cpumask_empty(&tmp) ? map_to_cpu(irq) : cpumask_first(&tmp);
> + cpuid = cpumask_first_and(affinity, cpu_online_mask);
> + cpuid = cpuid < nr_cpu_ids ? cpuid : map_to_cpu(irq);
> }
>
> return cpuid;
> --
> 2.27.0