xen: drop xen_sched_clock in favour of using plain wallclock time

xen_sched_clock only counts unstolen time.  In principle this should
be useful to the Linux scheduler so that it knows how much time a process
actually consumed.  But in practice this doesn't work very well as the
scheduler expects the sched_clock time to be synchronized between
cpus.  It also uses sched_clock to measure the time a task spends
sleeping, in which case "unstolen time" isn't meaningful.

So just use plain xen_clocksource_read to return wallclock nanoseconds
for sched_clock.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 399bed2..fef034a 100644 (file)
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -926,7 +926,7 @@ static const struct pv_init_ops xen_init_ops __initdata = {
 };
 
 static const struct pv_time_ops xen_time_ops __initdata = {
-       .sched_clock = xen_sched_clock,
+       .sched_clock = xen_clocksource_read,
 };
 
 static const struct pv_cpu_ops xen_cpu_ops __initdata = {

diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index 32764b8..e90360f 100644 (file)
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -155,45 +155,6 @@ static void do_stolen_accounting(void)
        account_idle_ticks(ticks);
 }
 
-/*
- * Xen sched_clock implementation.  Returns the number of unstolen
- * nanoseconds, which is nanoseconds the VCPU spent in RUNNING+BLOCKED
- * states.
- */
-unsigned long long xen_sched_clock(void)
-{
-       struct vcpu_runstate_info state;
-       cycle_t now;
-       u64 ret;
-       s64 offset;
-
-       /*
-        * Ideally sched_clock should be called on a per-cpu basis
-        * anyway, so preempt should already be disabled, but that's
-        * not current practice at the moment.
-        */
-       preempt_disable();
-
-       now = xen_clocksource_read();
-
-       get_runstate_snapshot(&state);
-
-       WARN_ON(state.state != RUNSTATE_running);
-
-       offset = now - state.state_entry_time;
-       if (offset < 0)
-               offset = 0;
-
-       ret = state.time[RUNSTATE_blocked] +
-               state.time[RUNSTATE_running] +
-               offset;
-
-       preempt_enable();
-
-       return ret;
-}
-
-
 /* Get the TSC speed from Xen */
 unsigned long xen_tsc_khz(void)
 {