On Sat, 2011-12-24 at 10:06 +0100, Mike Galbraith wrote:
> Greetings,
>
> I'm trying to convince 3.0-rt to perform on a 64 core box, and having a
> devil of a time with the darn thing. I have a wild theory that cores
> are much more closely synchronized in newer kernels, and that's causing
> massive QPI jabbering and xtime lock contention as cores bang
> cpupri_set() and ktime_get() in lockstep.
Seems not so wild a theory.
<idle>-0 [055] 1285.013088: mwait_idle <-cpu_idle
<idle>-0 [053] 1285.013860: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [043] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [053] 1285.013861: native_apic_mem_write <-smp_apic_timer_interrupt
<idle>-0 [044] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [043] 1285.013861: native_apic_mem_write <-smp_apic_timer_interrupt
<idle>-0 [061] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [054] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [038] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [053] 1285.013861: irq_enter <-smp_apic_timer_interrupt
<idle>-0 [044] 1285.013861: native_apic_mem_write <-smp_apic_timer_interrupt
<idle>-0 [043] 1285.013861: irq_enter <-smp_apic_timer_interrupt
<idle>-0 [008] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [032] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [051] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [024] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [054] 1285.013861: native_apic_mem_write <-smp_apic_timer_interrupt
<idle>-0 [038] 1285.013861: native_apic_mem_write <-smp_apic_timer_interrupt
<idle>-0 [053] 1285.013861: rcu_irq_enter <-irq_enter
<idle>-0 [044] 1285.013861: irq_enter <-smp_apic_timer_interrupt
<idle>-0 [045] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [006] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [043] 1285.013861: rcu_irq_enter <-irq_enter
<idle>-0 [029] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [014] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [032] 1285.013861: native_apic_mem_write <-smp_apic_timer_interrupt
<idle>-0 [042] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [031] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [051] 1285.013861: native_apic_mem_write <-smp_apic_timer_interrupt
<idle>-0 [024] 1285.013861: native_apic_mem_write <-smp_apic_timer_interrupt
<idle>-0 [054] 1285.013861: irq_enter <-smp_apic_timer_interrupt
<idle>-0 [015] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [027] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [038] 1285.013861: irq_enter <-smp_apic_timer_interrupt
<idle>-0 [044] 1285.013861: rcu_irq_enter <-irq_enter
<idle>-0 [053] 1285.013861: rcu_exit_nohz <-rcu_irq_enter
<idle>-0 [035] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [045] 1285.013861: native_apic_mem_write <-smp_apic_timer_interrupt
<idle>-0 [022] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [028] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [050] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [043] 1285.013861: rcu_exit_nohz <-rcu_irq_enter
<idle>-0 [049] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [061] 1285.013861: native_apic_mem_write <-smp_apic_timer_interrupt
<idle>-0 [019] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [032] 1285.013861: irq_enter <-smp_apic_timer_interrupt
<idle>-0 [029] 1285.013861: native_apic_mem_write <-smp_apic_timer_interrupt
<idle>-0 [014] 1285.013861: native_apic_mem_write <-smp_apic_timer_interrupt
<idle>-0 [024] 1285.013861: irq_enter <-smp_apic_timer_interrupt
<idle>-0 [042] 1285.013861: native_apic_mem_write <-smp_apic_timer_interrupt
<idle>-0 [039] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<idle>-0 [026] 1285.013861: smp_apic_timer_interrupt <-apic_timer_interrupt
<....snipage>
Guess I need to fight fire with fire. Make ticks jitter a little
somehow, so they don't make itimer wakeup jitter a truckload when it
collides with tick that is busy colliding with zillion other ticks.
'course that helps the real problem (dram sucks) not one bit.
-Mike
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