xen: drop xen_sched_clock in favour of using plain wallclock time

commit 8a22b9996b001c88f2bfb54c6de6a05fc39e177a upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 001c099471a57319e074c7faeb4f82d8d917e083..07e27f7b094a567c4ec39fb10e23aa394b3ed222 100644 (file)
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1179,7 +1179,7 @@ static const struct pv_time_ops xen_time_ops __initdata = {
        .set_wallclock = xen_set_wallclock,
        .get_wallclock = xen_get_wallclock,
        .get_tsc_khz = xen_tsc_khz,
-       .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 685b77470fc3612c45549018303808cb5cf628f3..d0f176ede6961f54d2b1b60a6b5da7613faed22c 100644 (file)
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -30,8 +30,6 @@
 #define TIMER_SLOP     100000
 #define NS_PER_TICK    (1000000000LL / HZ)
 
-static cycle_t xen_clocksource_read(void);
-
 /* runstate info updated by Xen */
 static DEFINE_PER_CPU(struct vcpu_runstate_info, runstate);
 
@@ -158,45 +156,6 @@ static void do_stolen_accounting(void)
        account_steal_time(idle_task(smp_processor_id()), 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)
 {
@@ -213,7 +172,7 @@ unsigned long xen_tsc_khz(void)
        return xen_khz;
 }
 
-static cycle_t xen_clocksource_read(void)
+cycle_t xen_clocksource_read(void)
 {
         struct pvclock_vcpu_time_info *src;
        cycle_t ret;

diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index dd3c23152a2e618f733192c86aac1ad04de61ed9..8a3c8234bf01661235117cadbfcbfd71c5680c95 100644 (file)
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -3,6 +3,7 @@
 
 #include <linux/init.h>
 #include <linux/irqreturn.h>
+#include <linux/clocksource.h>
 #include <xen/xen-ops.h>
 
 /* These are code, but not functions.  Defined in entry.S */
@@ -37,7 +38,7 @@ unsigned long xen_tsc_khz(void);
 void __init xen_time_init(void);
 unsigned long xen_get_wallclock(void);
 int xen_set_wallclock(unsigned long time);
-unsigned long long xen_sched_clock(void);
+cycle_t xen_clocksource_read(void);
 
 irqreturn_t xen_debug_interrupt(int irq, void *dev_id);