On Wed, Aug 07, 2013 at 07:40:15PM +0000, Christoph Lameter wrote: > On Wed, 7 Aug 2013, Kent Overstreet wrote: > > > I was breaking it apart because I was using this_cpu elsewhere too - for > > the bitmap of which cpus have non empty freelists. > > this_cpu can be retrieved with smp_processor_id(). > > > Or is this_cpu_ptr() doing something smarter than per_cpu_ptr(ptr, > > smp_processer_id())? There's so many variants I'm not 100% sure they're > > the same. > > Yes it is. It uses a sepecial register that contains the offset of this > cpus per cpu area instead of going through the table of all processor > offsets. Its less code.
Alright, well here's a fixup patch - untested for the moment though. One thing that was bugging me - I was never able to figure out for sure if smp_processor_id() returns a number in the range [0, nr_cpu_ids), at least I couldn't find where it was documented - could you tell me if that's true? >From e2b8016de49c28c0ccbe7849d7254f005c7e2e77 Mon Sep 17 00:00:00 2001 From: Kent Overstreet <[email protected]> Date: Wed, 7 Aug 2013 12:52:58 -0700 Subject: [PATCH] idr: Use this_cpu_ptr() for percpu_ida diff --git a/lib/idr.c b/lib/idr.c index fb374c3..320ffea 100644 --- a/lib/idr.c +++ b/lib/idr.c @@ -748,12 +748,10 @@ int percpu_ida_alloc(struct percpu_ida *pool, gfp_t gfp) DEFINE_WAIT(wait); struct percpu_ida_cpu *tags; unsigned long flags; - unsigned this_cpu; int tag; local_irq_save(flags); - this_cpu = smp_processor_id(); - tags = per_cpu_ptr(pool->tag_cpu, this_cpu); + tags = this_cpu_ptr(pool->tag_cpu); /* Fastpath */ tag = alloc_local_tag(pool, tags); @@ -782,7 +780,8 @@ int percpu_ida_alloc(struct percpu_ida *pool, gfp_t gfp) if (tags->nr_free) { tag = tags->freelist[--tags->nr_free]; if (tags->nr_free) - set_bit(this_cpu, pool->cpus_have_tags); + set_bit(smp_processor_id(), + pool->cpus_have_tags); } spin_unlock(&pool->ida.lock); @@ -794,8 +793,7 @@ int percpu_ida_alloc(struct percpu_ida *pool, gfp_t gfp) schedule(); local_irq_save(flags); - this_cpu = smp_processor_id(); - tags = per_cpu_ptr(pool->tag_cpu, this_cpu); + tags = this_cpu_ptr(pool->tag_cpu); } finish_wait(&pool->wait, &wait); @@ -814,13 +812,12 @@ void percpu_ida_free(struct percpu_ida *pool, unsigned tag) { struct percpu_ida_cpu *tags; unsigned long flags; - unsigned nr_free, this_cpu; + unsigned nr_free; BUG_ON(tag >= pool->nr_tags); local_irq_save(flags); - this_cpu = smp_processor_id(); - tags = per_cpu_ptr(pool->tag_cpu, this_cpu); + tags = this_cpu_ptr(pool->tag_cpu); spin_lock(&tags->lock); tags->freelist[tags->nr_free++] = tag; @@ -829,7 +826,8 @@ void percpu_ida_free(struct percpu_ida *pool, unsigned tag) spin_unlock(&tags->lock); if (nr_free == 1) { - set_bit(this_cpu, pool->cpus_have_tags); + set_bit(smp_processor_id(), + pool->cpus_have_tags); wake_up(&pool->wait); } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
