block: Remove the control of complete cpu from bio.

bio originally has the functionality to set the complete cpu, but
it is broken.

Chirstoph said that "This code is unused, and from the all the
discussions lately pretty obviously broken.  The only thing keeping
it serves is creating more confusion and possibly more bugs."

And Jens replied with "We can kill bio_set_completion_cpu(). I'm fine
with leaving cpu control to the request based drivers, they are the
only ones that can toggle the setting anyway".

So this patch tries to remove all the work of controling complete cpu
from a bio.

Cc: Shaohua Li <shaohua.li@intel.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Tao Ma <boyu.mt@taobao.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-core.c

@@ -1276,7 +1276,6 @@ static bool attempt_plug_merge(struct request_queue *q, struct bio *bio,
 
 void init_request_from_bio(struct request *req, struct bio *bio)
 {
-	req->cpu = bio->bi_comp_cpu;
 	req->cmd_type = REQ_TYPE_FS;
 
 	req->cmd_flags |= bio->bi_rw & REQ_COMMON_MASK;
@@ -1362,8 +1361,7 @@ void blk_queue_bio(struct request_queue *q, struct bio *bio)
 	 */
 	init_request_from_bio(req, bio);
 
-	if (test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags) ||
-	    bio_flagged(bio, BIO_CPU_AFFINE))
+	if (test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags))
 		req->cpu = raw_smp_processor_id();
 
 	plug = current->plug;

drivers/md/raid1.c

@@ -2172,7 +2172,6 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
 		bio->bi_next = NULL;
 		bio->bi_flags &= ~(BIO_POOL_MASK-1);
 		bio->bi_flags |= 1 << BIO_UPTODATE;
-		bio->bi_comp_cpu = -1;
 		bio->bi_rw = READ;
 		bio->bi_vcnt = 0;
 		bio->bi_idx = 0;

fs/bio.c

@@ -255,7 +255,6 @@ void bio_init(struct bio *bio)
 {
 	memset(bio, 0, sizeof(*bio));
 	bio->bi_flags = 1 << BIO_UPTODATE;
-	bio->bi_comp_cpu = -1;
 	atomic_set(&bio->bi_cnt, 1);
 }
 EXPORT_SYMBOL(bio_init);

include/linux/bio.h

@@ -268,14 +268,6 @@ extern struct bio_vec *bvec_alloc_bs(gfp_t, int, unsigned long *, struct bio_set
 extern void bvec_free_bs(struct bio_set *, struct bio_vec *, unsigned int);
 extern unsigned int bvec_nr_vecs(unsigned short idx);
 
-/*
- * Allow queuer to specify a completion CPU for this bio
- */
-static inline void bio_set_completion_cpu(struct bio *bio, unsigned int cpu)
-{
-	bio->bi_comp_cpu = cpu;
-}
-
 /*
  * bio_set is used to allow other portions of the IO system to
  * allocate their own private memory pools for bio and iovec structures.

include/linux/blk_types.h

@@ -59,8 +59,6 @@ struct bio {
 
 	unsigned int		bi_max_vecs;	/* max bvl_vecs we can hold */
 
-	unsigned int		bi_comp_cpu;	/* completion CPU */
-
 	atomic_t		bi_cnt;		/* pin count */
 
 	struct bio_vec		*bi_io_vec;	/* the actual vec list */
@@ -93,11 +91,10 @@ struct bio {
 #define BIO_BOUNCED	5	/* bio is a bounce bio */
 #define BIO_USER_MAPPED 6	/* contains user pages */
 #define BIO_EOPNOTSUPP	7	/* not supported */
-#define BIO_CPU_AFFINE	8	/* complete bio on same CPU as submitted */
-#define BIO_NULL_MAPPED 9	/* contains invalid user pages */
-#define BIO_FS_INTEGRITY 10	/* fs owns integrity data, not block layer */
-#define BIO_QUIET	11	/* Make BIO Quiet */
-#define BIO_MAPPED_INTEGRITY 12/* integrity metadata has been remapped */
+#define BIO_NULL_MAPPED 8	/* contains invalid user pages */
+#define BIO_FS_INTEGRITY 9	/* fs owns integrity data, not block layer */
+#define BIO_QUIET	10	/* Make BIO Quiet */
+#define BIO_MAPPED_INTEGRITY 11/* integrity metadata has been remapped */
 #define bio_flagged(bio, flag)	((bio)->bi_flags & (1 << (flag)))
 
 /*