From 9bcbdd9c58617f1301dd4f17c738bb9bc73aca70 Mon Sep 17 00:00:00 2001 From: Arjan van de Ven Date: Thu, 8 Oct 2009 06:40:41 -0700 Subject: x86, timers: Check for pending timers after (device) interrupts Now that range timers and deferred timers are common, I found a problem with these using the "perf timechart" tool. Frans Pop also reported high scheduler latencies via LatencyTop, when using iwlagn. It turns out that on x86, these two 'opportunistic' timers only get checked when another "real" timer happens. These opportunistic timers have the objective to save power by hitchhiking on other wakeups, as to avoid CPU wakeups by themselves as much as possible. The change in this patch runs this check not only at timer interrupts, but at all (device) interrupts. The effect is that: 1) the deferred timers/range timers get delayed less 2) the range timers cause less wakeups by themselves because the percentage of hitchhiking on existing wakeup events goes up. I've verified the working of the patch using "perf timechart", the original exposed bug is gone with this patch. Frans also reported success - the latencies are now down in the expected ~10 msec range. Signed-off-by: Arjan van de Ven Tested-by: Frans Pop Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Mike Galbraith LKML-Reference: <20091008064041.67219b13@infradead.org> Signed-off-by: Ingo Molnar --- arch/x86/kernel/irq.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'arch/x86/kernel/irq.c') diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c index 74656d1d4e3..39120619951 100644 --- a/arch/x86/kernel/irq.c +++ b/arch/x86/kernel/irq.c @@ -244,6 +244,7 @@ unsigned int __irq_entry do_IRQ(struct pt_regs *regs) __func__, smp_processor_id(), vector, irq); } + run_local_timers(); irq_exit(); set_irq_regs(old_regs); @@ -268,6 +269,7 @@ void smp_generic_interrupt(struct pt_regs *regs) if (generic_interrupt_extension) generic_interrupt_extension(); + run_local_timers(); irq_exit(); set_irq_regs(old_regs); -- cgit v1.2.3 From e7ab0f7b50bc4688fb5cf65de5d42e3b882fb8d1 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Fri, 9 Oct 2009 15:58:20 +0200 Subject: Revert "x86, timers: Check for pending timers after (device) interrupts" This reverts commit 9bcbdd9c58617f1301dd4f17c738bb9bc73aca70. The real bug producing LatencyTop latencies has been fixed in: f5dc375: sched: Update the clock of runqueue select_task_rq() selected And the commit being reverted here triggers local timer processing from every device IRQ. If device IRQs come in at a high frequency, this could cause a performance regression. The commit being reverted here purely 'fixed' the reported latency as a side effect, because CPUs were being moved out of idle more often. Acked-by: Peter Zijlstra Cc: Arjan van de Ven Cc: Frans Pop Cc: Linus Torvalds Cc: Mike Galbraith Cc: Thomas Gleixner LKML-Reference: <20091008064041.67219b13@infradead.org> Signed-off-by: Ingo Molnar --- arch/x86/kernel/irq.c | 2 -- 1 file changed, 2 deletions(-) (limited to 'arch/x86/kernel/irq.c') diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c index 39120619951..74656d1d4e3 100644 --- a/arch/x86/kernel/irq.c +++ b/arch/x86/kernel/irq.c @@ -244,7 +244,6 @@ unsigned int __irq_entry do_IRQ(struct pt_regs *regs) __func__, smp_processor_id(), vector, irq); } - run_local_timers(); irq_exit(); set_irq_regs(old_regs); @@ -269,7 +268,6 @@ void smp_generic_interrupt(struct pt_regs *regs) if (generic_interrupt_extension) generic_interrupt_extension(); - run_local_timers(); irq_exit(); set_irq_regs(old_regs); -- cgit v1.2.3 From 89ccf465abe6b20d804a63ae20307970c441369d Mon Sep 17 00:00:00 2001 From: Li Hong Date: Wed, 14 Oct 2009 18:50:39 +0800 Subject: x86, perf_event: Rename 'performance counter interrupt' In 'cdd6c482c9ff9c55475ee7392ec8f672eddb7be6', we renamed Performance Counters -> Performance Events. The name showed up in /proc/interrupts also needs a change. I use PMI (Performance monitoring interrupt) here, since it is the official name used in Intel's documents. Signed-off-by: Li Hong Cc: Andrew Morton Cc: Peter Zijlstra Cc: Paul Mackerras LKML-Reference: <20091014105039.GA22670@uhli> Signed-off-by: Ingo Molnar --- arch/x86/kernel/irq.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'arch/x86/kernel/irq.c') diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c index 39120619951..86fb2c8e065 100644 --- a/arch/x86/kernel/irq.c +++ b/arch/x86/kernel/irq.c @@ -63,10 +63,10 @@ static int show_other_interrupts(struct seq_file *p, int prec) for_each_online_cpu(j) seq_printf(p, "%10u ", irq_stats(j)->irq_spurious_count); seq_printf(p, " Spurious interrupts\n"); - seq_printf(p, "%*s: ", prec, "CNT"); + seq_printf(p, "%*s: ", prec, "PMI"); for_each_online_cpu(j) seq_printf(p, "%10u ", irq_stats(j)->apic_perf_irqs); - seq_printf(p, " Performance counter interrupts\n"); + seq_printf(p, " Performance monitoring interrupts\n"); seq_printf(p, "%*s: ", prec, "PND"); for_each_online_cpu(j) seq_printf(p, "%10u ", irq_stats(j)->apic_pending_irqs); -- cgit v1.2.3