linux-kernel - [PATCH] x86/apic: fix a printk precision vs width issue

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Message-Id: <1681301153-36849-1-git-send-email-lirongqing@baidu.com>
Date:   Wed, 12 Apr 2023 20:05:53 +0800
From:   Li RongQing <lirongqing@...du.com>
To:     lirongqing@...du.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
        pbonzini@...hat.com, sathyanarayanan.kuppuswamy@...ux.intel.com,
        linux-kernel@...r.kernel.org
Subject: [PATCH] x86/apic: fix a printk precision vs width issue

when HZ is 1000, host bus clock speed is 99812KHz, apic
shows 99.0812 MHz, since the width is 4 char but the max
remainder is 3 char when HZ is 1000
 [    0.136739] ..... calibration result: 99812
 [    0.136930] ..... host bus clock speed is 99.0812 MHz.

fix it by keeping 3 char width, and using 1000 as divisor
and the result is below:
 [    0.136930] ..... host bus clock speed is 99.812 MHz.

Signed-off-by: Li RongQing <lirongqing@...du.com>
---
 arch/x86/kernel/apic/apic.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 20d9a60..7e3b1bf 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -948,15 +948,15 @@ static int __init calibrate_APIC_clock(void)
 
 	if (boot_cpu_has(X86_FEATURE_TSC)) {
 		apic_printk(APIC_VERBOSE, "..... CPU clock speed is "
-			    "%ld.%04ld MHz.\n",
-			    (deltatsc / LAPIC_CAL_LOOPS) / (1000000 / HZ),
-			    (deltatsc / LAPIC_CAL_LOOPS) % (1000000 / HZ));
+			    "%ld.%03ld MHz.\n",
+			    ((deltatsc) / LAPIC_CAL_LOOPS) * HZ / 1000 / 1000,
+			    ((deltatsc) / LAPIC_CAL_LOOPS) * HZ / 1000 % 1000);
 	}
 
 	apic_printk(APIC_VERBOSE, "..... host bus clock speed is "
-		    "%u.%04u MHz.\n",
-		    lapic_timer_period / (1000000 / HZ),
-		    lapic_timer_period % (1000000 / HZ));
+		    "%u.%03u MHz.\n",
+		    (lapic_timer_period * HZ / 1000) / 1000,
+		    (lapic_timer_period * HZ / 1000) % 1000);
 
 	/*
 	 * Do a sanity check on the APIC calibration result
-- 
2.9.4