Re: [PATCH] Add migration_cost option to scheduler

["Yang, Xiaowei" <xiaowei.yang@intel.com>]

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Yang, Xiaowei wrote:
> Tian, Kevin wrote:
>>> From: George Dunlap
>>> Sent: Monday, March 09, 2009 8:56 PM
>>>
>>> Hmm, I think this patch may not be exactly what we want.  It looks
>>> like it checks for how long a vcpu has been in its current stat, not
>>> how recently it has been running.  So if a vcpu sleeps for a long time
>>> on a cpu that's running other workloads, then wakes up
>>> (blocked->runnable), the cache is by no means "hot".  But since it has
>>> only been in the "runnable" state for a few hundred cycles, it won't
>>> be migrated, even though there's little cost.
>> Then to add a per-vcpu last_running_timestamp which is recorded when 
>> vcpu is scheduled out, could hit the purpose here?
> Yes, it's more reasonable. I can make a patch.
> 

The patch is attached. Had a quick test using the previous config and 
saw no obvious different result with it. May be explained by the fact 
that the benchmarks has no many IO operations - db and logfile are put 
to ramdisk for sysbench test. Anyway it's closer to what we really want. 
Thanks both of you!

Signed-off-by: Xiaowei Yang <xiaowei.yang@intel.com>

Thanks,
xiaowei

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diff -r 115c97f32dc6 xen/common/sched_credit.c
--- a/xen/common/sched_credit.c	Tue Mar 10 00:18:39 2009 +0800
+++ b/xen/common/sched_credit.c	Tue Mar 10 03:09:44 2009 +0800
@@ -328,7 +328,7 @@ static inline int
 static inline int
 __csched_vcpu_is_cache_hot(struct vcpu *v)
 {
-    int hot = ((NOW() - v->runstate.state_entry_time) <
+    int hot = ((NOW() - v->last_run_time) <
                ((uint64_t)vcpu_migration_delay * 1000u));
 
     if ( hot )
diff -r 115c97f32dc6 xen/common/schedule.c
--- a/xen/common/schedule.c	Tue Mar 10 00:18:39 2009 +0800
+++ b/xen/common/schedule.c	Tue Mar 10 03:00:36 2009 +0800
@@ -836,6 +836,7 @@ static void schedule(void)
         (test_bit(_VPF_blocked, &prev->pause_flags) ? RUNSTATE_blocked :
          (vcpu_runnable(prev) ? RUNSTATE_runnable : RUNSTATE_offline)),
         now);
+    prev->last_run_time = now;
 
     ASSERT(next->runstate.state != RUNSTATE_running);
     vcpu_runstate_change(next, RUNSTATE_running, now);
diff -r 115c97f32dc6 xen/include/xen/sched.h
--- a/xen/include/xen/sched.h	Tue Mar 10 00:18:39 2009 +0800
+++ b/xen/include/xen/sched.h	Tue Mar 10 02:59:15 2009 +0800
@@ -102,6 +102,9 @@ struct vcpu
     } runstate_guest; /* guest address */
 #endif
 
+    /* last time when vCPU is scheduled out */
+    uint64_t last_run_time;
+
     /* Has the FPU been initialised? */
     bool_t           fpu_initialised;
     /* Has the FPU been used since it was last saved? */

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