The following test:
sudo taskset -c 0 t/io_uring -b512 -d128 -c32 -s32 -p1 -F1 -B1 /dev/nullb0
reports 1366 K IOPS on my test setup without this patch and 1380 K IOPS
with this patch applied. In other words, this patch realizes a 1%
performance improvement. I think this is because this patch makes the
compiler generate better code. See also commit da521626ac62 ("bio:
optimize initialization of a bio").
The assembler code generated by gcc without this patch is as follows:
0x0000000000000000 <+0>: call 0x5 <bio_init+5>
0x0000000000000005 <+5>: xor %eax,%eax
0x0000000000000007 <+7>: xor %ecx,%ecx
0x0000000000000009 <+9>: movl $0x1,0x1c(%rdi)
0x0000000000000010 <+16>: movq $0x0,(%rdi)
0x0000000000000017 <+23>: movq $0x0,0x8(%rdi)
0x000000000000001f <+31>: movq $0x0,0x10(%rdi)
0x0000000000000027 <+39>: mov %ax,0x18(%rdi)
0x000000000000002b <+43>: movb $0x0,0x1a(%rdi)
0x000000000000002f <+47>: movq $0x0,0x20(%rdi)
0x0000000000000037 <+55>: movq $0x0,0x28(%rdi)
0x000000000000003f <+63>: movl $0x0,0x30(%rdi)
0x0000000000000046 <+70>: movq $0x0,0x38(%rdi)
0x000000000000004e <+78>: movq $0x0,0x40(%rdi)
0x0000000000000056 <+86>: movq $0x0,0x48(%rdi)
0x000000000000005e <+94>: movq $0x0,0x50(%rdi)
0x0000000000000066 <+102>: movq $0x0,0x58(%rdi)
0x000000000000006e <+110>: movq $0x0,0x60(%rdi)
0x0000000000000076 <+118>: mov %cx,0x68(%rdi)
0x000000000000007a <+122>: movl $0x1,0x6c(%rdi)
0x0000000000000081 <+129>: mov %dx,0x6a(%rdi)
0x0000000000000085 <+133>: mov %rsi,0x70(%rdi)
0x0000000000000089 <+137>: movq $0x0,0x78(%rdi)
0x0000000000000091 <+145>: ret
With this patch bio_init() is compiled into the following assembly code:
0x0000000000000000 <+0>: call 0x5 <bio_init+5>
0x0000000000000005 <+5>: mov %rdi,%r8
0x0000000000000008 <+8>: mov $0x10,%ecx
0x000000000000000d <+13>: xor %eax,%eax
0x000000000000000f <+15>: rep stos %rax,%es:(%rdi)
0x0000000000000012 <+18>: movl $0x1,0x1c(%r8)
0x000000000000001a <+26>: mov %dx,0x6a(%r8)
0x000000000000001f <+31>: movl $0x1,0x6c(%r8)
0x0000000000000027 <+39>: mov %rsi,0x70(%r8)
0x000000000000002b <+43>: ret
Cc: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
block/bio.c | 45 ++++++++-------------------------------------
1 file changed, 8 insertions(+), 37 deletions(-)
diff --git a/block/bio.c b/block/bio.c
index 5df3dd282e40..775cd4274523 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -244,47 +244,18 @@ static void bio_free(struct bio *bio)
}
/*
- * Users of this function have their own bio allocation. Subsequently,
- * they must remember to pair any call to bio_init() with bio_uninit()
- * when IO has completed, or when the bio is released.
+ * Users of this function must pair any call to bio_init() with a call to
+ * bio_uninit() after IO has completed or when the bio is released.
*/
void bio_init(struct bio *bio, struct bio_vec *table,
unsigned short max_vecs)
{
- bio->bi_next = NULL;
- bio->bi_bdev = NULL;
- bio->bi_opf = 0;
- bio->bi_flags = 0;
- bio->bi_ioprio = 0;
- bio->bi_write_hint = 0;
- bio->bi_status = 0;
- bio->bi_iter.bi_sector = 0;
- bio->bi_iter.bi_size = 0;
- bio->bi_iter.bi_idx = 0;
- bio->bi_iter.bi_bvec_done = 0;
- bio->bi_end_io = NULL;
- bio->bi_private = NULL;
-#ifdef CONFIG_BLK_CGROUP
- bio->bi_blkg = NULL;
- bio->bi_issue.value = 0;
-#ifdef CONFIG_BLK_CGROUP_IOCOST
- bio->bi_iocost_cost = 0;
-#endif
-#endif
-#ifdef CONFIG_BLK_INLINE_ENCRYPTION
- bio->bi_crypt_context = NULL;
-#endif
-#ifdef CONFIG_BLK_DEV_INTEGRITY
- bio->bi_integrity = NULL;
-#endif
- bio->bi_vcnt = 0;
-
- atomic_set(&bio->__bi_remaining, 1);
- atomic_set(&bio->__bi_cnt, 1);
-
- bio->bi_max_vecs = max_vecs;
- bio->bi_io_vec = table;
- bio->bi_pool = NULL;
+ *bio = (struct bio) {
+ .__bi_remaining = ATOMIC_INIT(1),
+ .__bi_cnt = ATOMIC_INIT(1),
+ .bi_max_vecs = max_vecs,
+ .bi_io_vec = table,
+ };
}
EXPORT_SYMBOL(bio_init);
