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hrtimer: Tune hrtimer_interrupt hang logic

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The hrtimer_interrupt hang logic adjusts min_delta_ns based on the
execution time of the hrtimer callbacks.

This is error-prone for virtual machines, where a guest vcpu can be
scheduled out during the execution of the callbacks (and the callbacks
themselves can do operations that translate to blocking operations in
the hypervisor), which in can lead to large min_delta_ns rendering the
system unusable.

Replace the current heuristics with something more reliable. Allow the
interrupt code to try 3 times to catch up with the lost time. If that
fails use the total time spent in the interrupt handler to defer the
next timer interrupt so the system can catch up with other things
which got delayed. Limit that deferment to 100ms.

The retry events and the maximum time spent in the interrupt handler
are recorded and exposed via /proc/timer_list

Inspired by a patch from Marcelo.

Reported-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Marcelo Tosatti <mtosatti@redhat.com>
Cc: kvm@vger.kernel.org
This commit is contained in:
Thomas Gleixner
2009-11-13 17:05:44 +01:00
parent 3067e02f8f
commit 41d2e49493
3 changed files with 70 additions and 45 deletions
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5
kernel/time/timer_list.c
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@@ -150,6 +150,9 @@ static void print_cpu(struct seq_file *m, int cpu, u64 now)
P_ns(expires_next);
P(hres_active);
P(nr_events);
P(nr_retries);
P(nr_hangs);
P_ns(max_hang_time);
#endif
#undef P
#undef P_ns
@@ -254,7 +257,7 @@ static int timer_list_show(struct seq_file *m, void *v)
u64 now = ktime_to_ns(ktime_get());
int cpu;
SEQ_printf(m, "Timer List Version: v0.4\n");
SEQ_printf(m, "Timer List Version: v0.5\n");
SEQ_printf(m, "HRTIMER_MAX_CLOCK_BASES: %d\n", HRTIMER_MAX_CLOCK_BASES);
SEQ_printf(m, "now at %Ld nsecs\n", (unsigned long long)now);