diff options
| author | Shaohua Li <shli@kernel.org> | 2013-12-31 11:38:27 +0800 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2014-01-30 12:57:25 -0700 |
| commit | d835502f3dacad1638d516ab156d66f0ba377cf5 (patch) | |
| tree | 1a82543b7c14120251a4bceaa08f5cc9f86ecf43 /lib | |
| parent | 53d8ab29f8f6d67e37857b68189b38fa3d87dd8e (diff) | |
| download | lwn-d835502f3dacad1638d516ab156d66f0ba377cf5.tar.gz lwn-d835502f3dacad1638d516ab156d66f0ba377cf5.zip | |
percpu_ida: fix a live lock
steal_tags only happens when free tags is more than half of the total
tags. This is too strict and can cause live lock. I found that if one
cpu has free tags, but other cpu can't steal (thread is bound to
specific cpus), threads which want 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), no performance changes were
observed.
Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/percpu_ida.c | 7 |
1 files changed, 2 insertions, 5 deletions
diff --git a/lib/percpu_ida.c b/lib/percpu_ida.c index 9d054bf91d0f..85f43b1718d4 100644 --- a/lib/percpu_ida.c +++ b/lib/percpu_ida.c @@ -54,9 +54,7 @@ static inline void move_tags(unsigned *dst, unsigned *dst_nr, /* * 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 percpu_ida *pool, 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) { |