From ca7c6076baed396737e31e33b87a637d70e9fc5f Mon Sep 17 00:00:00 2001
From: Dou Liyang <douly.fnst@cn.fujitsu.com>
Date: Wed, 13 Sep 2017 17:12:51 +0800
Subject: [PATCH] x86/ioapic: Refactor the delay logic in timer_irq_works()
timer_irq_works() is used to detects the timer IRQs. It calls mdelay(10) to
delay ten ticks and check whether the timer IRQ work or not.
mdelay() depends on the loops_per_jiffy which is set up in
calibrate_delay(), but the delay calibration depends on a working timer
interrupt, which causes a chicken and egg problem.
The correct solution is to set up the interrupt mode and making sure that
the timer interrupt is delivered correctly before invoking calibrate_delay().
That means that mdelay() cannot be used in timer_irq_works().
Provide helper functions to make a rough delay estimate which is good enough
to prove that the timer interrupt is working. Either use TSC or a simple
delay loop and assume that 4GHz is the maximum CPU frequency to base the
delay calculation on.
Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: yinghai@kernel.org
Cc: bhe@redhat.com
Link: https://lkml.kernel.org/r/1505293975-26005-9-git-send-email-douly.fnst@cn.fujitsu.com
---
arch/x86/kernel/apic/io_apic.c | 45 ++++++++++++++++++++++++++++++++--
1 file changed, 43 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 70e48aa6af98..f8f248749c56 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -1585,6 +1585,43 @@ static int __init notimercheck(char *s)
}
__setup("no_timer_check", notimercheck);
+static void __init delay_with_tsc(void)
+{
+ unsigned long long start, now;
+ unsigned long end = jiffies + 4;
+
+ start = rdtsc();
+
+ /*
+ * We don't know the TSC frequency yet, but waiting for
+ * 40000000000/HZ TSC cycles is safe:
+ * 4 GHz == 10 jiffies
+ * 1 GHz == 40 jiffies
+ */
+ do {
+ rep_nop();
+ now = rdtsc();
+ } while ((now - start) < 40000000000UL / HZ &&
+ time_before_eq(jiffies, end));
+}
+
+static void __init delay_without_tsc(void)
+{
+ unsigned long end = jiffies + 4;
+ int band = 1;
+
+ /*
+ * We don't know any frequency yet, but waiting for
+ * 40940000000/HZ cycles is safe:
+ * 4 GHz == 10 jiffies
+ * 1 GHz == 40 jiffies
+ * 1 << 1 + 1 << 2 +...+ 1 << 11 = 4094
+ */
+ do {
+ __delay(((1U << band++) * 10000000UL) / HZ);
+ } while (band < 12 && time_before_eq(jiffies, end));
+}
+
/*
* There is a nasty bug in some older SMP boards, their mptable lies
* about the timer IRQ. We do the following to work around the situation:
@@ -1603,8 +1640,12 @@ static int __init timer_irq_works(void)
local_save_flags(flags);
local_irq_enable();
- /* Let ten ticks pass... */
- mdelay((10 * 1000) / HZ);
+
+ if (boot_cpu_has(X86_FEATURE_TSC))
+ delay_with_tsc();
+ else
+ delay_without_tsc();
+
local_irq_restore(flags);
/*
--
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