- Currently, sched_balance_pair() may cause a CPU to send an IPI_PREEMPT to

  itself, which sparc64 hardware doesn't support. One way to solve this
  would be to directly call sched_preempt() instead of issuing a self-IPI.
  However, quoting jhb@:
  "On the other hand, you can probably just skip the IPI entirely if we are
  going to send it to the current CPU.  Presumably, once this routine
  finishes, the current CPU will exit softlock (or will do so "soon") and
  will then pick the next thread to run based on the adjustments made in
  this routine, so there's no need to IPI the CPU running this routine
  anyway.  I think this is the better solution.  Right now what is probably
  happening on other platforms is as soon as this routine finishes the CPU
  processes its self-IPI and causes mi_switch() which will just switch back
  to the softclock thread it is already running."
- With r226054 and the the above change in place, sparc64 now no longer is
  incompatible with ULE and vice versa. However, powerpc/E500 still is.

Submitted by:	jhb
Reviewed by:	jeff

1 files changed, 9 insertions, 4 deletions

diff --git a/sys/kern/sched_ule.c b/sys/kern/sched_ule.c
index f505676..31d3d11 100644
--- a/sys/kern/sched_ule.c
+++ b/sys/kern/sched_ule.c
@@ -76,7 +76,7 @@ dtrace_vtime_switch_func_t	dtrace_vtime_switch_func;
 #include <machine/cpu.h>
 #include <machine/smp.h>
 
-#if defined(__sparc64__)
+#if defined(__powerpc__) && defined(E500)
 #error "This architecture is not currently compatible with ULE"
 #endif
 
@@ -839,6 +839,7 @@ sched_balance_pair(struct tdq *high, struct tdq *low)
 	int low_load;
 	int moved;
 	int move;
+	int cpu;
 	int diff;
 	int i;
 
@@ -860,10 +861,14 @@ sched_balance_pair(struct tdq *high, struct tdq *low)
 		for (i = 0; i < move; i++)
 			moved += tdq_move(high, low);
 		/*
-		 * IPI the target cpu to force it to reschedule with the new
-		 * workload.
+		 * In case the target isn't the current cpu IPI it to force a
+		 * reschedule with the new workload.
 		 */
-		ipi_cpu(TDQ_ID(low), IPI_PREEMPT);
+		cpu = TDQ_ID(low);
+		sched_pin();
+		if (cpu != PCPU_GET(cpuid))
+			ipi_cpu(cpu, IPI_PREEMPT);
+		sched_unpin();
 	}
 	tdq_unlock_pair(high, low);
 	return (moved);