[PATCH] Dynamic sched domains: cpuset changes

Adds the core update_cpu_domains code and updated cpusets documentation

Signed-off-by: Dinakar Guniguntala <dino@in.ibm.com>
Acked-by: Paul Jackson <pj@sgi.com>
Acked-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/Documentation/cpusets.txt b/Documentation/cpusets.txt
index 2f8f24e..ad944c0 100644 (file)
--- a/Documentation/cpusets.txt
+++ b/Documentation/cpusets.txt
@@ -51,6 +51,14 @@ mems_allowed vector.
 
 If a cpuset is cpu or mem exclusive, no other cpuset, other than a direct
 ancestor or descendent, may share any of the same CPUs or Memory Nodes.
+A cpuset that is cpu exclusive has a sched domain associated with it.
+The sched domain consists of all cpus in the current cpuset that are not
+part of any exclusive child cpusets.
+This ensures that the scheduler load balacing code only balances
+against the cpus that are in the sched domain as defined above and not
+all of the cpus in the system. This removes any overhead due to
+load balancing code trying to pull tasks outside of the cpu exclusive
+cpuset only to be prevented by the tasks' cpus_allowed mask.
 
 User level code may create and destroy cpusets by name in the cpuset
 virtual file system, manage the attributes and permissions of these
@@ -84,6 +92,9 @@ This can be especially valuable on:
       and a database), or
     * NUMA systems running large HPC applications with demanding
       performance characteristics.
+    * Also cpu_exclusive cpusets are useful for servers running orthogonal
+      workloads such as RT applications requiring low latency and HPC
+      applications that are throughput sensitive
 
 These subsets, or "soft partitions" must be able to be dynamically
 adjusted, as the job mix changes, without impacting other concurrently
@@ -125,6 +136,8 @@ Cpusets extends these two mechanisms as follows:
  - A cpuset may be marked exclusive, which ensures that no other
    cpuset (except direct ancestors and descendents) may contain
    any overlapping CPUs or Memory Nodes.
+   Also a cpu_exclusive cpuset would be associated with a sched
+   domain.
  - You can list all the tasks (by pid) attached to any cpuset.
 
 The implementation of cpusets requires a few, simple hooks
@@ -136,6 +149,9 @@ into the rest of the kernel, none in performance critical paths:
    allowed in that tasks cpuset.
  - in sched.c migrate_all_tasks(), to keep migrating tasks within
    the CPUs allowed by their cpuset, if possible.
+ - in sched.c, a new API partition_sched_domains for handling
+   sched domain changes associated with cpu_exclusive cpusets
+   and related changes in both sched.c and arch/ia64/kernel/domain.c
  - in the mbind and set_mempolicy system calls, to mask the requested
    Memory Nodes by what's allowed in that tasks cpuset.
  - in page_alloc, to restrict memory to allowed nodes.

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 79dd929..984c0bf 100644 (file)
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -595,10 +595,62 @@ static int validate_change(const struct cpuset *cur, const struct cpuset *trial)
        return 0;
 }
 
+/*
+ * For a given cpuset cur, partition the system as follows
+ * a. All cpus in the parent cpuset's cpus_allowed that are not part of any
+ *    exclusive child cpusets
+ * b. All cpus in the current cpuset's cpus_allowed that are not part of any
+ *    exclusive child cpusets
+ * Build these two partitions by calling partition_sched_domains
+ *
+ * Call with cpuset_sem held.  May nest a call to the
+ * lock_cpu_hotplug()/unlock_cpu_hotplug() pair.
+ */
+static void update_cpu_domains(struct cpuset *cur)
+{
+       struct cpuset *c, *par = cur->parent;
+       cpumask_t pspan, cspan;
+
+       if (par == NULL || cpus_empty(cur->cpus_allowed))
+               return;
+
+       /*
+        * Get all cpus from parent's cpus_allowed not part of exclusive
+        * children
+        */
+       pspan = par->cpus_allowed;
+       list_for_each_entry(c, &par->children, sibling) {
+               if (is_cpu_exclusive(c))
+                       cpus_andnot(pspan, pspan, c->cpus_allowed);
+       }
+       if (is_removed(cur) || !is_cpu_exclusive(cur)) {
+               cpus_or(pspan, pspan, cur->cpus_allowed);
+               if (cpus_equal(pspan, cur->cpus_allowed))
+                       return;
+               cspan = CPU_MASK_NONE;
+       } else {
+               if (cpus_empty(pspan))
+                       return;
+               cspan = cur->cpus_allowed;
+               /*
+                * Get all cpus from current cpuset's cpus_allowed not part
+                * of exclusive children
+                */
+               list_for_each_entry(c, &cur->children, sibling) {
+                       if (is_cpu_exclusive(c))
+                               cpus_andnot(cspan, cspan, c->cpus_allowed);
+               }
+       }
+
+       lock_cpu_hotplug();
+       partition_sched_domains(&pspan, &cspan);
+       unlock_cpu_hotplug();
+}
+
 static int update_cpumask(struct cpuset *cs, char *buf)
 {
        struct cpuset trialcs;
-       int retval;
+       int retval, cpus_unchanged;
 
        trialcs = *cs;
        retval = cpulist_parse(buf, trialcs.cpus_allowed);
@@ -608,9 +660,13 @@ static int update_cpumask(struct cpuset *cs, char *buf)
        if (cpus_empty(trialcs.cpus_allowed))
                return -ENOSPC;
        retval = validate_change(cs, &trialcs);
-       if (retval == 0)
-               cs->cpus_allowed = trialcs.cpus_allowed;
-       return retval;
+       if (retval < 0)
+               return retval;
+       cpus_unchanged = cpus_equal(cs->cpus_allowed, trialcs.cpus_allowed);
+       cs->cpus_allowed = trialcs.cpus_allowed;
+       if (is_cpu_exclusive(cs) && !cpus_unchanged)
+               update_cpu_domains(cs);
+       return 0;
 }
 
 static int update_nodemask(struct cpuset *cs, char *buf)
@@ -646,7 +702,7 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs, char *buf)
 {
        int turning_on;
        struct cpuset trialcs;
-       int err;
+       int err, cpu_exclusive_changed;
 
        turning_on = (simple_strtoul(buf, NULL, 10) != 0);
 
@@ -657,13 +713,18 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs, char *buf)
                clear_bit(bit, &trialcs.flags);
 
        err = validate_change(cs, &trialcs);
-       if (err == 0) {
-               if (turning_on)
-                       set_bit(bit, &cs->flags);
-               else
-                       clear_bit(bit, &cs->flags);
-       }
-       return err;
+       if (err < 0)
+               return err;
+       cpu_exclusive_changed =
+               (is_cpu_exclusive(cs) != is_cpu_exclusive(&trialcs));
+       if (turning_on)
+               set_bit(bit, &cs->flags);
+       else
+               clear_bit(bit, &cs->flags);
+
+       if (cpu_exclusive_changed)
+                update_cpu_domains(cs);
+       return 0;
 }
 
 static int attach_task(struct cpuset *cs, char *buf)
@@ -1309,12 +1370,14 @@ static int cpuset_rmdir(struct inode *unused_dir, struct dentry *dentry)
                up(&cpuset_sem);
                return -EBUSY;
        }
-       spin_lock(&cs->dentry->d_lock);
        parent = cs->parent;
        set_bit(CS_REMOVED, &cs->flags);
+       if (is_cpu_exclusive(cs))
+               update_cpu_domains(cs);
        list_del(&cs->sibling); /* delete my sibling from parent->children */
        if (list_empty(&parent->children))
                check_for_release(parent);
+       spin_lock(&cs->dentry->d_lock);
        d = dget(cs->dentry);
        cs->dentry = NULL;
        spin_unlock(&d->d_lock);