linux-kernel - [PATCH v2] powerpc/xive: Use cpumask

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Message-ID: <20240926092623.399577-2-costa.shul@redhat.com>
Date: Thu, 26 Sep 2024 12:26:22 +0300
From: Costa Shulyupin <costa.shul@...hat.com>
To: Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Naveen N Rao <naveen@...nel.org>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Ming Lei <ming.lei@...hat.com>,
	Costa Shulyupin <costa.shul@...hat.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2] powerpc/xive: Use cpumask_intersects()

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@...hat.com>
Reviewed-by: Ming Lei <ming.lei@...hat.com>

---

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