Re: [PATCH 2.6.13-rc6] cpu_exclusive sched domains build fix

Paul Jackson
2005-08-24T20:31:20Z

Nick wrote:
> I get the feeling that exclusive cpusets should just be
> completely disabled for 2.6.13

No no - not disable exclusive cpusets - disable using them to try
to define sched domains.

That is, I hope you mean that Dinakar's patch that uses cpu_exclusive
cpusets to define sched domains should be disabled for 2.6.13. For
what they were worth (not a whole lot, granted), cpu_exclusive cpusets
have been in the kernel since 2.6.12. They just didn't have any affect
in the placement of sched domains. So long as they continue to do not
a whole lot, I see more risk than gain in disabling them for 2.6.13.

So long as the cpuset code stops making any calls to partition_sched_domains()
whatsoever, then we should be back where we were in 2.6.12, so far as the
scheduler is concerned - right?

I hope that the following (untested, unbuilt) patch, that I suggested
in my "Mon, 22 Aug 2005 13:38:23 -0700" message best meets you
suggestion above ... and I quote:

==========

The safest, mind numbingly simple thing to do that would avoid the oops
that Hawkes reported is to simply not have the cpuset code call the
code to setup a dynamic sched domain. This is choice (2) above, and
could be done at the last hour with relative safety.

Here is an untested patch that does (2):

=====

Index: linux-2.6.13-cpuset-mempolicy-migrate/kernel/cpuset.c
===================================================================
--- linux-2.6.13-cpuset-mempolicy-migrate.orig/kernel/cpuset.c
+++ linux-2.6.13-cpuset-mempolicy-migrate/kernel/cpuset.c
@@ -627,6 +627,15 @@ static int validate_change(const struct
* Call with cpuset_sem held. May nest a call to the
* lock_cpu_hotplug()/unlock_cpu_hotplug() pair.
*/
+
+/*
+ * Hack to avoid 2.6.13 partial node dynamic sched domain bug.
+ * Disable letting 'cpu_exclusive' cpusets define dynamic sched
+ * domains, until the sched domain can handle partial nodes.
+ * Remove this ifdef hackery when sched domains fixed.
+ */
+#define DISABLE_EXCLUSIVE_CPU_DOMAINS 1
+#ifdef DISABLE_EXCLUSIVE_CPU_DOMAINS
static void update_cpu_domains(struct cpuset *cur)
{
struct cpuset *c, *par = cur->parent;
@@ -667,6 +676,11 @@ static void update_cpu_domains(struct cp
partition_sched_domains(&pspan, &cspan);
unlock_cpu_hotplug();
}
+#else
+static void update_cpu_domains(struct cpuset *cur)
+{
+}
+#endif

static int update_cpumask(struct cpuset *cs, char *buf)
{

=====

--
I won't rest till it's the best ...
Programmer, Linux Scalability
Paul Jackson <pj@sgi.com> 1.925.600.0401