kernel.git/arch/s390/kernel/vtime.c, branch linux-2.6.37.y

[S390] nohz/s390: fix arch_needs_cpu() return value on offline cpus

2010-12-01T09:08:17Z

This fixes the same problem as described in the patch "nohz: fix printk_needs_cpu() return value on offline cpus" for the arch_needs_cpu() primitive: arch_needs_cpu() may return 1 if called on offline cpus. When a cpu gets offlined it schedules the idle process which, before killing its own cpu, will call tick_nohz_stop_sched_tick(). That function in turn will call arch_needs_cpu() in order to check if the local tick can be disabled. On offline cpus this function should naturally return 0 since regardless if the tick gets disabled or not the cpu will be dead short after. That is besides the fact that __cpu_disable() should already have made sure that no interrupts on the offlined cpu will be delivered anyway. In this case it prevents tick_nohz_stop_sched_tick() to call select_nohz_load_balancer(). No idea if that really is a problem. However what made me debug this is that on 2.6.32 the function get_nohz_load_balancer() is used within __mod_timer() to select a cpu on which a timer gets enqueued. If arch_needs_cpu() returns 1 then the nohz_load_balancer cpu doesn't get updated when a cpu gets offlined. It may contain the cpu number of an offline cpu. In turn timers get enqueued on an offline cpu and not very surprisingly they never expire and cause system hangs. This has been observed 2.6.32 kernels. On current kernels __mod_timer() uses get_nohz_timer_target() which doesn't have that problem. However there might be other problems because of the too early exit tick_nohz_stop_sched_tick() in case a cpu goes offline. This specific bug was indrocuded with 3c5d92a0 "nohz: Introduce arch_needs_cpu". In this case a cpu hotplug notifier is used to fix the issue in order to keep the normal/fast path small. All we need to do is to clear the condition that makes arch_needs_cpu() return 1 since it is just a performance improvement which is supposed to keep the local tick running for a short period if a cpu goes idle. Nothing special needs to be done except for clearing the condition. Cc: stable@kernel.org Acked-by: Peter Zijlstra Signed-off-by: Heiko Carstens Signed-off-by: Martin Schwidefsky

[S390] cleanup lowcore access from external interrupts

2010-10-25T14:10:19Z

Read external interrupts parameters from the lowcore in the first level interrupt handler in entry[64].S. Signed-off-by: Martin Schwidefsky

[S390] idle time accounting vs. machine checks

2010-05-17T08:00:15Z

A machine check can interrupt the i/o and external interrupt handler anytime. If the machine check occurs while the interrupt handler is waking up from idle vtime_start_cpu can get executed a second time and the int_clock / async_enter_timer values in the lowcore get clobbered. This can confuse the cpu time accounting. To fix this problem two changes are needed. First the machine check handler has to use its own copies of int_clock and async_enter_timer, named mcck_clock and mcck_enter_timer. Second the nested execution of vtime_start_cpu has to be prevented. This is done in s390_idle_check by checking the wait bit in the program status word. Signed-off-by: Martin Schwidefsky

nohz: Introduce arch_needs_cpu

2009-11-05T06:53:53Z

Allow the architecture to request a normal jiffy tick when the system goes idle and tick_nohz_stop_sched_tick is called . On s390 the hook is used to prevent the system going fully idle if there has been an interrupt other than a clock comparator interrupt since the last wakeup. On s390 the HiperSockets response time for 1 connection ping-pong goes down from 42 to 34 microseconds. The CPU cost decreases by 27%. Signed-off-by: Martin Schwidefsky LKML-Reference: <20090929122533.402715150@de.ibm.com> Signed-off-by: Thomas Gleixner

[S390] lockless idle time accounting

2009-06-22T10:08:23Z

Replace the spinlock used in the idle time accounting with a sequence counter mechanism analog to seqlock. Signed-off-by: Martin Schwidefsky

[S390] time: convert from bootmem to slab

2009-06-22T10:08:16Z

The slab allocator is earlier available so convert the bootmem allocations to slab/gfp allocations. Signed-off-by: Heiko Carstens Signed-off-by: Martin Schwidefsky

[S390] merge cpu.h into cputime.h

2009-06-12T08:27:29Z

All definition in cpu.h have to do with cputime accounting. Move them to cputime.h and remove the header file. Signed-off-by: Martin Schwidefsky

[S390] /proc/stat idle field for idle cpus

2009-04-23T11:58:17Z

The cpu idle field in the output of /proc/stat is too small for cpus that have been idle for more than a tick. Add the architecture hook arch_idle_time that allows to add the not accounted idle time of a sleeping cpu without waking the cpu. The s390 implementation of arch_idle_time uses the already existing s390_idle_data per_cpu variable to find the sleep time of a neighboring idle cpu. Signed-off-by: Martin Schwidefsky

[S390] boot cputime accounting

2009-04-14T13:37:27Z

Start the cpu time accounting very early to catch the cpu time spent for the initial kernel setup. To make the output of /proc/uptime match the sum of all cpu accounting values of the boot cpu reset xtime and wall_to_monotonic to sane values based on the TOD clock. The values set by timekeeping_init are off by up to a second. Signed-off-by: Martin Schwidefsky

[S390] fix idle time accounting

2009-04-14T13:37:26Z

The steal time is calculated by subtracting the time the virtual cpu has been running on a physical cpu from the wall clock time. To make that work all wall time needs to be added to the steal time field first before the virtual cpu time is subtracted. The time between the last clock update and the load of the enabled wait psw needs to be added to the steal_time field as well to make the sum over all cpu accounting numbers match the wall clock. Signed-off-by: Martin Schwidefsky