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Subject[PATCH 14/25] xen: xen: deal with negative stolen time
Stolen time should never be negative; if it ever is, it probably
indicates some other bug. However, if it does happen, then its better
to just clamp it at zero, rather than trying to account for it as a
huge positive number.

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

---
arch/i386/xen/time.c | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)
===================================================================
--- a/arch/i386/xen/time.c
+++ b/arch/i386/xen/time.c
@@ -77,7 +77,7 @@ static void do_stolen_accounting(void)
{
struct vcpu_runstate_info state;
struct vcpu_runstate_info *snap;
- u64 blocked, runnable, offline, stolen;
+ s64 blocked, runnable, offline, stolen;
cputime_t ticks;

get_runstate_snapshot(&state);
@@ -97,6 +97,10 @@ static void do_stolen_accounting(void)
including any left-overs from last time. Passing NULL to
account_steal_time accounts the time as stolen. */
stolen = runnable + offline + __get_cpu_var(residual_stolen);
+
+ if (stolen < 0)
+ stolen = 0;
+
ticks = 0;
while(stolen >= NS_PER_TICK) {
ticks++;
@@ -109,6 +113,10 @@ static void do_stolen_accounting(void)
including any left-overs from last time. Passing idle to
account_steal_time accounts the time as idle/wait. */
blocked += __get_cpu_var(residual_blocked);
+
+ if (blocked < 0)
+ blocked = 0;
+
ticks = 0;
while(blocked >= NS_PER_TICK) {
ticks++;
@@ -127,7 +135,8 @@ unsigned long long xen_sched_clock(void)
{
struct vcpu_runstate_info state;
cycle_t now;
- unsigned long long ret;
+ u64 ret;
+ s64 offset;

/*
* Ideally sched_clock should be called on a per-cpu basis
@@ -142,9 +151,13 @@ unsigned long long xen_sched_clock(void)

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] +
- (now - state.state_entry_time);
+ offset;

preempt_enable();

--

-
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