2020-01-20 10:06:01

by Wen Yang

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

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 <[email protected]>
Cc: Paolo Valente <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: [email protected]
Cc: [email protected]
---
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

2020-01-22 17:35:52

by Jens Axboe

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

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