steal_tags only happens when free tags is more than half of the total tags.
This is too restrict and can cause live lock. I found one cpu has free tags,
but other cpu can't steal (thread is bound to specific cpus), threads which
wants to allocate tags are always sleeping. I found this when I run next patch,
but this could happen without it I think.
I did performance test too with null_blk. Two cases (each cpu has enough percpu
tags, or total tags are limited) haven't performance changes.
Signed-off-by: Shaohua Li <s...@fusionio.com>
---
lib/percpu_ida.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
Index: linux/lib/percpu_ida.c
===================================================================
--- linux.orig/lib/percpu_ida.c 2013-11-25 09:36:52.196626486 +0800
+++ linux/lib/percpu_ida.c 2013-12-31 11:20:03.205400612 +0800
@@ -54,9 +54,7 @@ static inline void move_tags(unsigned *d
/*
* Try to steal tags from a remote cpu's percpu freelist.
*
- * We first check how many percpu freelists have tags - we don't steal tags
- * unless enough percpu freelists have tags on them that it's possible more
than
- * half the total tags could be stuck on remote percpu freelists.
+ * We first check how many percpu freelists have tags
*
* Then we iterate through the cpus until we find some tags - we don't attempt
* to find the "best" cpu to steal from, to keep cacheline bouncing to a
@@ -69,8 +67,7 @@ static inline void steal_tags(struct per
struct percpu_ida_cpu *remote;
for (cpus_have_tags = cpumask_weight(&pool->cpus_have_tags);
- cpus_have_tags * pool->percpu_max_size > pool->nr_tags / 2;
- cpus_have_tags--) {
+ cpus_have_tags; cpus_have_tags--) {
cpu = cpumask_next(cpu, &pool->cpus_have_tags);
if (cpu >= nr_cpu_ids) {
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
