From ca7c6076baed396737e31e33b87a637d70e9fc5f Mon Sep 17 00:00:00 2001 From: Dou Liyang 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 Signed-off-by: Thomas Gleixner 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); /* -- GitLab