Siddha, Suresh B wrote:
On Fri, Apr 15, 2005 at 11:03:20PM +1000, Nick Piggin wrote:
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c 2005-04-15 22:52:25.000000000 +1000
+++ linux-2.6/kernel/sched.c 2005-04-15 22:58:54.000000000 +1000
@@ -4844,7 +4844,14 @@ static int __devinit sd_parent_degenerat
/* WAKE_BALANCE is a subset of WAKE_AFFINE */
if (cflags & SD_WAKE_AFFINE)
pflags &= ~SD_WAKE_BALANCE;
- if ((~sd->flags) & parent->flags)
+ /* Flags needing groups don't count if only 1 group in parent */
+ if (parent->groups == parent->groups->next) {
+ pflags &= ~(SD_LOAD_BALANCE |
+ SD_BALANCE_NEWIDLE |
+ SD_BALANCE_FORK |
+ SD_BALANCE_EXEC);
+ }
This patch works fine and I like this fix. But should n't we be adding
SD_WAKE_AFFINE and SD_WAKE_BALANCE to this list?
Hmm, well they don't use groups, but I guess they can be excluded,
because if the parent span is the same as the child span (and that
is true at this point), then SD_WAKE_AFFFINE/BALANCE in the parent
will never be executed. Good point.
wake_idle should be doing a similar thing too, but that needs a bit
of work.
And about SD_BALANCE_FORK, now that we have multi level sbe/sbf, we should
add this flag to SD_CPU/SIBLING_INIT too..
I guess we should think about it. It depends - does SD_BALANCE_FORK
make sense on a plain SMP machine? If so, then it probably makes
sense to be in the 'SMP' domain on a NUMA system, otherwise not.
I suspect that for BALANCE_FORK, the answer may be no. On an SMP, it
is far less disastrous to misplace tasks and have them picked up by
the periodic rebalancer. What's more, BALANCE_FORK does add a non
trivial overhead when moving tasks to other CPUs.
But it's open for debate. I haven't done comprehensive tests.
--
SUSE Labs, Novell Inc.
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