[PATCH v2] powerpc/xive: Use cpumask_intersects()

From: Costa Shulyupin
Date: Thu Sep 26 2024 - 05:27:23 EST


Replace `cpumask_any_and(a, b) >= nr_cpu_ids`
with the more readable `!cpumask_intersects(a, b)`.

Comparison between cpumask_any_and() and cpumask_intersects()

The cpumask_any_and() function expands using FIND_FIRST_BIT(),
resulting in a loop that iterates through each bit of the bitmask:

for (idx = 0; idx * BITS_PER_LONG < sz; idx++) {
val = (FETCH);
if (val) {
sz = min(idx * BITS_PER_LONG + __ffs(MUNGE(val)), sz);
break;
}
}

The cpumask_intersects() function expands using __bitmap_intersects(),
resulting in that the first loop iterates through each long word of the bitmask,
and the second through each bit within a long word:

unsigned int k, lim = bits/BITS_PER_LONG;
for (k = 0; k < lim; ++k)
if (bitmap1[k] & bitmap2[k])
return true;

if (bits % BITS_PER_LONG)
if ((bitmap1[k] & bitmap2[k]) & BITMAP_LAST_WORD_MASK(bits))
return true;

Conclusion: cpumask_intersects() is at least as efficient as cpumask_any_and(),
if not more so, as it typically performs fewer loops and comparisons.

Signed-off-by: Costa Shulyupin <costa.shul@xxxxxxxxxx>
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>

---

v2: add comparison between cpumask_any_and() and cpumask_intersects()

---
arch/powerpc/sysdev/xive/common.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/sysdev/xive/common.c b/arch/powerpc/sysdev/xive/common.c
index fa01818c1972c..a6c388bdf5d08 100644
--- a/arch/powerpc/sysdev/xive/common.c
+++ b/arch/powerpc/sysdev/xive/common.c
@@ -726,7 +726,7 @@ static int xive_irq_set_affinity(struct irq_data *d,
pr_debug("%s: irq %d/0x%x\n", __func__, d->irq, hw_irq);

/* Is this valid ? */
- if (cpumask_any_and(cpumask, cpu_online_mask) >= nr_cpu_ids)
+ if (!cpumask_intersects(cpumask, cpu_online_mask))
return -EINVAL;

/*
--
2.45.0