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block: optimise in irq bio put caching

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When enlisting a bio into ->free_list_irq we protect the list by
disabling irqs. It's likely they're already disabled and performance of
local_irq_{save,restore}() is decent, but it's not zero cost.

Let's only use the irq cache when when we're serving a hard irq, which
allows to remove local_irq_{save,restore}(), and fall back to bio_free()
in all left cases.

Profiles indicate that the bio_put() cost is reduced by ~3.5 times
(1.76% -> 0.49%), and total throughput of a CPU bound benchmark improve
by around 1% (t/io_uring with high QD and several drives).

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/36d207540b7046c653cc16e5ff08fe7234b19f81.1707314970.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2024-02-07 14:14:29 +00:00 committed by Jens Axboe
parent c9f5f3aa19
commit e516c3fc6c
1 changed files with 12 additions and 11 deletions
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23
block/bio.c
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@ -762,30 +762,31 @@ static inline void bio_put_percpu_cache(struct bio *bio)
struct bio_alloc_cache *cache;
cache = per_cpu_ptr(bio->bi_pool->cache, get_cpu());
if (READ_ONCE(cache->nr_irq) + cache->nr > ALLOC_CACHE_MAX) {
put_cpu();
bio_free(bio);
return;
}
bio_uninit(bio);
if (READ_ONCE(cache->nr_irq) + cache->nr > ALLOC_CACHE_MAX)
goto out_free;
if (in_task()) {
bio_uninit(bio);
bio->bi_next = cache->free_list;
/* Not necessary but helps not to iopoll already freed bios */
bio->bi_bdev = NULL;
cache->free_list = bio;
cache->nr++;
} else {
unsigned long flags;
} else if (in_hardirq()) {
lockdep_assert_irqs_disabled();
local_irq_save(flags);
bio_uninit(bio);
bio->bi_next = cache->free_list_irq;
cache->free_list_irq = bio;
cache->nr_irq++;
local_irq_restore(flags);
} else {
goto out_free;
}
put_cpu();
return;
out_free:
put_cpu();
bio_free(bio);
}
/**