Re: volanoMark regression with kernel 2.6.26-rc1

Srivatsa Vaddagiri
2008-05-14T13:35:30Z

On Mon, May 12, 2008 at 11:20:47AM +0200, Peter Zijlstra wrote:
> It looks like things like find_busiest_group() just think everything is
> peachy when the imbalance is < 1 task - which with all this grouping
> stuff is not necessarily true.

fwiw, the following hack seems to help bring down regression to ~5%
(b/n 2.6.25 and 2.6.26-rc1 with USER_SCHED):

Also in the patch GROUP_SCALE can probably be less than what I used (and
needs a ifdef GROUP_SCHED) ..

Not-signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>

---
kernel/sched.c | 4 ++++
kernel/sched_fair.c | 14 +++++---------
kernel/sched_features.h | 2 +-
3 files changed, 10 insertions(+), 10 deletions(-)

Index: current/kernel/sched.c
===================================================================
--- current.orig/kernel/sched.c
+++ current/kernel/sched.c
@@ -1551,13 +1551,17 @@ static void cpuacct_charge(struct task_s
static inline void cpuacct_charge(struct task_struct *tsk, u64 cputime) {}
#endif

+#define GROUP_SCALE (2*1024)
+
static inline void inc_cpu_load(struct rq *rq, unsigned long load)
{
+ load *= GROUP_SCALE;
update_load_add(&rq->load, load);
}

static inline void dec_cpu_load(struct rq *rq, unsigned long load)
{
+ load *= GROUP_SCALE;
update_load_sub(&rq->load, load);
}

Index: current/kernel/sched_fair.c
===================================================================
--- current.orig/kernel/sched_fair.c
+++ current/kernel/sched_fair.c
@@ -1393,24 +1393,20 @@ load_balance_fair(struct rq *this_rq, in
unsigned long this_weight, busiest_weight;
long rem_load, max_load, moved_load;

+ busiest_weight = tg->cfs_rq[busiest_cpu]->task_weight;
/*
* empty group
*/
- if (!aggregate(tg, sd)->task_weight)
+ if (!aggregate(tg, sd)->task_weight || !busiest_weight)
continue;

rem_load = rem_load_move * aggregate(tg, sd)->rq_weight;
rem_load /= aggregate(tg, sd)->load + 1;

- this_weight = tg->cfs_rq[this_cpu]->task_weight;
- busiest_weight = tg->cfs_rq[busiest_cpu]->task_weight;
-
- imbalance = (busiest_weight - this_weight) / 2;
-
- if (imbalance < 0)
- imbalance = busiest_weight;
+ if (!rem_load)
+ continue;

- max_load = max(rem_load, imbalance);
+ max_load = rem_load;
moved_load = __load_balance_fair(this_rq, this_cpu, busiest,
max_load, sd, idle, all_pinned, this_best_prio,
tg->cfs_rq[busiest_cpu]);
Index: current/kernel/sched_features.h
===================================================================
--- current.orig/kernel/sched_features.h
+++ current/kernel/sched_features.h
@@ -6,5 +6,5 @@ SCHED_FEAT(CACHE_HOT_BUDDY, 1)
SCHED_FEAT(SYNC_WAKEUPS, 1)
SCHED_FEAT(HRTICK, 1)
SCHED_FEAT(DOUBLE_TICK, 0)
-SCHED_FEAT(NORMALIZED_SLEEPER, 1)
+SCHED_FEAT(NORMALIZED_SLEEPER, 0)
SCHED_FEAT(DEADLINE, 1)

--
Regards,
vatsa