[PATCH] sched: add option to serialize load balancing

Large sched domains can be very expensive to scan.  Add an option SD_SERIALIZE
to the sched domain flags.  If that flag is set then we make sure that no
other such domain is being balanced.

[akpm@osdl.org: build fix]
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Cc: Peter Williams <pwil3058@bigpond.net.au>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
Cc: "Chen, Kenneth W" <kenneth.w.chen@intel.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/include/asm-i386/topology.h b/include/asm-i386/topology.h
index 978d095..ac58580 100644 (file)
--- a/include/asm-i386/topology.h
+++ b/include/asm-i386/topology.h
@@ -89,6 +89,7 @@ static inline int node_to_first_cpu(int node)
        .flags                  = SD_LOAD_BALANCE       \
                                | SD_BALANCE_EXEC       \
                                | SD_BALANCE_FORK       \
+                               | SD_SERIALIZE          \
                                | SD_WAKE_BALANCE,      \
        .last_balance           = jiffies,              \
        .balance_interval       = 1,                    \

diff --git a/include/asm-ia64/topology.h b/include/asm-ia64/topology.h
index a6e3856..22ed674 100644 (file)
--- a/include/asm-ia64/topology.h
+++ b/include/asm-ia64/topology.h
@@ -101,6 +101,7 @@ void build_cpu_to_node_map(void);
        .flags                  = SD_LOAD_BALANCE       \
                                | SD_BALANCE_EXEC       \
                                | SD_BALANCE_FORK       \
+                               | SD_SERIALIZE          \
                                | SD_WAKE_BALANCE,      \
        .last_balance           = jiffies,              \
        .balance_interval       = 64,                   \

diff --git a/include/asm-powerpc/topology.h b/include/asm-powerpc/topology.h
index 50c0140..6610495 100644 (file)
--- a/include/asm-powerpc/topology.h
+++ b/include/asm-powerpc/topology.h
@@ -66,6 +66,7 @@ static inline int pcibus_to_node(struct pci_bus *bus)
                                | SD_BALANCE_EXEC       \
                                | SD_BALANCE_NEWIDLE    \
                                | SD_WAKE_IDLE          \
+                               | SD_SERIALIZE          \
                                | SD_WAKE_BALANCE,      \
        .last_balance           = jiffies,              \
        .balance_interval       = 1,                    \

diff --git a/include/asm-x86_64/topology.h b/include/asm-x86_64/topology.h
index 5c8f492..2facec5 100644 (file)
--- a/include/asm-x86_64/topology.h
+++ b/include/asm-x86_64/topology.h
@@ -47,6 +47,7 @@ extern int __node_distance(int, int);
        .flags                  = SD_LOAD_BALANCE       \
                                | SD_BALANCE_FORK       \
                                | SD_BALANCE_EXEC       \
+                               | SD_SERIALIZE          \
                                | SD_WAKE_BALANCE,      \
        .last_balance           = jiffies,              \
        .balance_interval       = 1,                    \

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 1208fea..ea92e5c 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -648,6 +648,7 @@ enum idle_type
 #define SD_SHARE_CPUPOWER      128     /* Domain members share cpu power */
 #define SD_POWERSAVINGS_BALANCE        256     /* Balance for power savings */
 #define SD_SHARE_PKG_RESOURCES 512     /* Domain members share cpu pkg resources */
+#define SD_SERIALIZE           1024    /* Only a single load balancing instance */
 
 #define BALANCE_FOR_MC_POWER   \
        (sched_smt_power_savings ? SD_POWERSAVINGS_BALANCE : 0)

diff --git a/include/linux/topology.h b/include/linux/topology.h
index b93bb6c..6c5a6e6 100644 (file)
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -194,7 +194,8 @@
        .wake_idx               = 0, /* unused */       \
        .forkexec_idx           = 0, /* unused */       \
        .per_cpu_gain           = 100,                  \
-       .flags                  = SD_LOAD_BALANCE,      \
+       .flags                  = SD_LOAD_BALANCE       \
+                               | SD_SERIALIZE, \
        .last_balance           = jiffies,              \
        .balance_interval       = 64,                   \
        .nr_balance_failed      = 0,                    \

diff --git a/kernel/sched.c b/kernel/sched.c
index 0a4a26b..2b2b780 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2880,6 +2880,7 @@ static void update_load(struct rq *this_rq)
  *
  * Balancing parameters are set up in arch_init_sched_domains.
  */
+static DEFINE_SPINLOCK(balancing);
 
 static void run_rebalance_domains(struct softirq_action *h)
 {
@@ -2909,6 +2910,11 @@ static void run_rebalance_domains(struct softirq_action *h)
                if (unlikely(!interval))
                        interval = 1;
 
+               if (sd->flags & SD_SERIALIZE) {
+                       if (!spin_trylock(&balancing))
+                               goto out;
+               }
+
                if (time_after_eq(jiffies, sd->last_balance + interval)) {
                        if (load_balance(this_cpu, this_rq, sd, idle)) {
                                /*
@@ -2920,6 +2926,9 @@ static void run_rebalance_domains(struct softirq_action *h)
                        }
                        sd->last_balance = jiffies;
                }
+               if (sd->flags & SD_SERIALIZE)
+                       spin_unlock(&balancing);
+out:
                if (time_after(next_balance, sd->last_balance + interval))
                        next_balance = sd->last_balance + interval;
        }