diff mbox series

xen/cpupool: limit number of cpupools

Message ID 20220518144410.6806-1-jgross@suse.com (mailing list archive)
State New
Headers show
Series xen/cpupool: limit number of cpupools | expand

Commit Message

Juergen Gross May 18, 2022, 2:44 p.m. UTC
Today the number of cpupools in a system is unlimited. This can lead to
multiple problems (e.g. duplicate cpupool-id).

Limit the number of cpupools to twice the number of maximum possible
cpus, allowing to have one cpupool per physical cpu plus some spare
cpupools for special means (there are already existing use cases for
such spare cpupools).

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 xen/common/sched/cpupool.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

Comments

Andrew Cooper May 18, 2022, 2:58 p.m. UTC | #1
On 18/05/2022 15:44, Juergen Gross wrote:
> Today the number of cpupools in a system is unlimited. This can lead to
> multiple problems (e.g. duplicate cpupool-id).

Not to mention scalability issues.  Search by ID is O(n).

>
> Limit the number of cpupools to twice the number of maximum possible
> cpus, allowing to have one cpupool per physical cpu plus some spare
> cpupools for special means (there are already existing use cases for
> such spare cpupools).

Probably one of Suggested-by/Reported-by/Requested-by :)  Dealers choice.

> Signed-off-by: Juergen Gross <jgross@suse.com>

Otherwise, LGTM.

Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
diff mbox series

Patch

diff --git a/xen/common/sched/cpupool.c b/xen/common/sched/cpupool.c
index f6e3d97e52..7cc25ee8b4 100644
--- a/xen/common/sched/cpupool.c
+++ b/xen/common/sched/cpupool.c
@@ -30,6 +30,7 @@  struct cpupool *cpupool0;                /* Initial cpupool with Dom0 */
 cpumask_t cpupool_free_cpus;             /* cpus not in any cpupool */
 
 static LIST_HEAD(cpupool_list);          /* linked list, sorted by poolid */
+static unsigned int n_cpupools;
 
 static int cpupool_moving_cpu = -1;
 static struct cpupool *cpupool_cpu_moving = NULL;
@@ -276,6 +277,14 @@  static struct cpupool *cpupool_create(unsigned int poolid,
 
     spin_lock(&cpupool_lock);
 
+    /* Don't allow too many cpupools. */
+    if ( n_cpupools >= 2 * nr_cpu_ids )
+    {
+        ret = -ENOSPC;
+        goto unlock;
+    }
+    n_cpupools++;
+
     if ( poolid != CPUPOOLID_NONE )
     {
         q = __cpupool_find_by_id(poolid, false);
@@ -332,7 +341,9 @@  static struct cpupool *cpupool_create(unsigned int poolid,
 
  err:
     list_del(&c->list);
+    n_cpupools--;
 
+ unlock:
     spin_unlock(&cpupool_lock);
 
     free_cpupool_struct(c);
@@ -356,6 +367,7 @@  static int cpupool_destroy(struct cpupool *c)
         return -EBUSY;
     }
 
+    n_cpupools--;
     list_del(&c->list);
 
     spin_unlock(&cpupool_lock);