linux-kernel - [PATCH 01/13] kernel/irq/proc: use seq_put_decimal_ull

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Message-Id: <20241108160717.9547-1-00107082@163.com>
Date: Sat,  9 Nov 2024 00:07:17 +0800
From: David Wang <00107082@....com>
To: tglx@...utronix.de
Cc: linux-kernel@...r.kernel.org,
	David Wang <00107082@....com>
Subject: [PATCH 01/13] kernel/irq/proc: use seq_put_decimal_ull_width() for decimal values

seq_printf() is costy, on a system with m interrupts and n CPUs, there
would be m*n decimal values yield via seq_printf() when reading
/proc/interrupts, the cost parsing format strings grows with number of
CPU. Profiling on a x86 8-core system indicates seq_printf() takes ~47%
samples of show_interrupts(), and replace seq_printf() with
seq_put_decimal_ull_width() could have near 30% performance gain.

The improvement has pratical significance, considering many monitoring
tools would read /proc/interrupts periodically.

Signed-off-by: David Wang <00107082@....com>
---
 kernel/irq/proc.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/irq/proc.c b/kernel/irq/proc.c
index 9081ada81c3d..988ce781e813 100644
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -494,9 +494,11 @@ int show_interrupts(struct seq_file *p, void *v)
 	if (!desc->action || irq_desc_is_chained(desc) || !desc->kstat_irqs)
 		goto outsparse;

-	seq_printf(p, "%*d: ", prec, i);
+	seq_printf(p, "%*d:", prec, i);
 	for_each_online_cpu(j)
-		seq_printf(p, "%10u ", desc->kstat_irqs ? per_cpu(desc->kstat_irqs->cnt, j) : 0);
+		seq_put_decimal_ull_width(p, " ",
+					  desc->kstat_irqs ? per_cpu(desc->kstat_irqs->cnt, j) : 0,
+					  10);

 	raw_spin_lock_irqsave(&desc->lock, flags);
 	if (desc->irq_data.chip) {
-- 
2.39.2