[PATCH] block, bfq: improve arithmetic division in bfq_delta()

[PATCH] block, bfq: improve arithmetic division in bfq_delta()

[Wen Yang]

do_div() does a 64-by-32 division. Use div64_ul() instead of it
if the divisor is unsigned long, to avoid truncation to 32-bit.
And as a nice side effect also cleans up the function a bit.

Signed-off-by: Wen Yang <wenyang@linux.alibaba.com>
Cc: Paolo Valente <paolo.valente@linaro.org>
Cc: Jens Axboe <axboe@fb.com>
Cc: linux-block@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
 block/bfq-wf2q.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c
index 05f0bf4a1144..ffe9ce9faa89 100644
--- a/block/bfq-wf2q.c
+++ b/block/bfq-wf2q.c
@@ -277,10 +277,7 @@ struct bfq_queue *bfq_entity_to_bfqq(struct bfq_entity *entity)
  */
 static u64 bfq_delta(unsigned long service, unsigned long weight)
 {
-	u64 d = (u64)service << WFQ_SERVICE_SHIFT;
-
-	do_div(d, weight);
-	return d;
+	return div64_ul((u64)service << WFQ_SERVICE_SHIFT, weight);
 }
 
 /**
-- 
2.23.0

Re: [PATCH] block, bfq: improve arithmetic division in bfq_delta()

[Jens Axboe]

On 1/20/20 3:04 AM, Wen Yang wrote:
> do_div() does a 64-by-32 division. Use div64_ul() instead of it
> if the divisor is unsigned long, to avoid truncation to 32-bit.
> And as a nice side effect also cleans up the function a bit.

Applied, thanks.

-- 
Jens Axboe