nohz: Introduce arch_needs_cpu
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 <schwidefsky@de.ibm.com>
LKML-Reference: <20090929122533.402715150@de.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/arch/s390/kernel/s390_ext.c b/arch/s390/kernel/s390_ext.c
index 0de305b..59618bc 100644
--- a/arch/s390/kernel/s390_ext.c
+++ b/arch/s390/kernel/s390_ext.c
@@ -126,6 +126,8 @@
/* Serve timer interrupts first. */
clock_comparator_work();
kstat_cpu(smp_processor_id()).irqs[EXTERNAL_INTERRUPT]++;
+ if (code != 0x1004)
+ __get_cpu_var(s390_idle).nohz_delay = 1;
index = ext_hash(code);
for (p = ext_int_hash[index]; p; p = p->next) {
if (likely(p->code == code))
diff --git a/arch/s390/kernel/vtime.c b/arch/s390/kernel/vtime.c
index c41bb0d..b59a812 100644
--- a/arch/s390/kernel/vtime.c
+++ b/arch/s390/kernel/vtime.c
@@ -167,6 +167,8 @@
/* Wait for external, I/O or machine check interrupt. */
psw.mask = psw_kernel_bits | PSW_MASK_WAIT | PSW_MASK_IO | PSW_MASK_EXT;
+ idle->nohz_delay = 0;
+
/* Check if the CPU timer needs to be reprogrammed. */
if (vq->do_spt) {
__u64 vmax = VTIMER_MAX_SLICE;