blk-throttle: correct calculation of wait time in tg_may_dispatch

In C language, When executing "if (expression1 && expression2)" and
expression1 return false, the expression2 may not be executed.
For "tg_within_bps_limit(tg, bio, bps_limit, &bps_wait) &&
tg_within_iops_limit(tg, bio, iops_limit, &iops_wait))", if bps is
limited, tg_within_bps_limit will return false and
tg_within_iops_limit will not be called. So even bps and iops are
both limited, iops_wait will not be calculated and is always zero.
So wait time of iops is always ignored.

Fix this by always calling tg_within_bps_limit and tg_within_iops_limit
to get wait time for both bps and iops.

Observed that:
1. Wait time in tg_within_iops_limit/tg_within_bps_limit need always
be stored as wait argument is always passed.
2. wait time is stored to zero if iops/bps is limited otherwise non-zero
is stored.
Simpfy tg_within_iops_limit/tg_within_bps_limit by removing wait argument
and return wait time directly. Caller tg_may_dispatch checks if wait time
is zero to find if iops/bps is limited.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Kemeng Shi <shikemeng@huawei.com>
Link: https://lore.kernel.org/r/20221205115709.251489-5-shikemeng@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 75010110d481ad4efcfe7697262dc54621d7122e..d5b7a2354ad7d7aaa211064e19286c5c3c37d2e8 100644 (file)
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -822,17 +822,15 @@ static void tg_update_carryover(struct throtl_grp *tg)
                   tg->carryover_ios[READ], tg->carryover_ios[WRITE]);
 }
 
-static bool tg_within_iops_limit(struct throtl_grp *tg, struct bio *bio,
-                                u32 iops_limit, unsigned long *wait)
+static unsigned long tg_within_iops_limit(struct throtl_grp *tg, struct bio *bio,
+                                u32 iops_limit)
 {
        bool rw = bio_data_dir(bio);
        unsigned int io_allowed;
        unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
 
        if (iops_limit == UINT_MAX) {
-               if (wait)
-                       *wait = 0;
-               return true;
+               return 0;
        }
 
        jiffy_elapsed = jiffies - tg->slice_start[rw];
@@ -842,21 +840,16 @@ static bool tg_within_iops_limit(struct throtl_grp *tg, struct bio *bio,
        io_allowed = calculate_io_allowed(iops_limit, jiffy_elapsed_rnd) +
                     tg->carryover_ios[rw];
        if (tg->io_disp[rw] + 1 <= io_allowed) {
-               if (wait)
-                       *wait = 0;
-               return true;
+               return 0;
        }
 
        /* Calc approx time to dispatch */
        jiffy_wait = jiffy_elapsed_rnd - jiffy_elapsed;
-
-       if (wait)
-               *wait = jiffy_wait;
-       return false;
+       return jiffy_wait;
 }
 
-static bool tg_within_bps_limit(struct throtl_grp *tg, struct bio *bio,
-                               u64 bps_limit, unsigned long *wait)
+static unsigned long tg_within_bps_limit(struct throtl_grp *tg, struct bio *bio,
+                               u64 bps_limit)
 {
        bool rw = bio_data_dir(bio);
        u64 bytes_allowed, extra_bytes;
@@ -865,9 +858,7 @@ static bool tg_within_bps_limit(struct throtl_grp *tg, struct bio *bio,
 
        /* no need to throttle if this bio's bytes have been accounted */
        if (bps_limit == U64_MAX || bio_flagged(bio, BIO_BPS_THROTTLED)) {
-               if (wait)
-                       *wait = 0;
-               return true;
+               return 0;
        }
 
        jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
@@ -880,9 +871,7 @@ static bool tg_within_bps_limit(struct throtl_grp *tg, struct bio *bio,
        bytes_allowed = calculate_bytes_allowed(bps_limit, jiffy_elapsed_rnd) +
                        tg->carryover_bytes[rw];
        if (tg->bytes_disp[rw] + bio_size <= bytes_allowed) {
-               if (wait)
-                       *wait = 0;
-               return true;
+               return 0;
        }
 
        /* Calc approx time to dispatch */
@@ -897,9 +886,7 @@ static bool tg_within_bps_limit(struct throtl_grp *tg, struct bio *bio,
         * up we did. Add that time also.
         */
        jiffy_wait = jiffy_wait + (jiffy_elapsed_rnd - jiffy_elapsed);
-       if (wait)
-               *wait = jiffy_wait;
-       return false;
+       return jiffy_wait;
 }
 
 /*
@@ -947,8 +934,9 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
                                jiffies + tg->td->throtl_slice);
        }
 
-       if (tg_within_bps_limit(tg, bio, bps_limit, &bps_wait) &&
-           tg_within_iops_limit(tg, bio, iops_limit, &iops_wait)) {
+       bps_wait = tg_within_bps_limit(tg, bio, bps_limit);
+       iops_wait = tg_within_iops_limit(tg, bio, iops_limit);
+       if (bps_wait + iops_wait == 0) {
                if (wait)
                        *wait = 0;
                return true;