On 2022/5/16 18:19, Chengming Zhou wrote:
> For an active leaf node, its inuse shouldn't be zero or exceed
> its active, but it's not true when deactivate idle iocg or delete
> iocg in ioc_pd_free().
>
> Although inuse of 1 is very small, it could cause noticeable hwi
> decrease in the long running server. So we'd better fix it.
>
> And check iocg->child_active_sum is enough for inner iocg, remove
> the needless list_empty check by the way.
>
> Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
> ---
> block/blk-iocost.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/block/blk-iocost.c b/block/blk-iocost.c
> index 2570732b92d1..84374ebcc402 100644
> --- a/block/blk-iocost.c
> +++ b/block/blk-iocost.c
> @@ -1073,11 +1073,11 @@ static void __propagate_weights(struct ioc_gq *iocg, u32 active, u32 inuse,
> * @active. An active internal node's inuse is solely determined by the
> * inuse to active ratio of its children regardless of @inuse.
> */
> - if (list_empty(&iocg->active_list) && iocg->child_active_sum) {
> + if (iocg->child_active_sum) {
> inuse = DIV64_U64_ROUND_UP(active * iocg->child_inuse_sum,
> iocg->child_active_sum);
> } else {
> - inuse = clamp_t(u32, inuse, 1, active);
> + inuse = clamp_t(u32, inuse, 0, active);
I found the commit message is wrong after a second look at the test data,
inuse value will be zero when active is zero, since:
#define clamp_t(type, val, lo, hi) min_t(type, max_t(type, val, lo), hi)
So clamp_t(u32, 0, 1, 0) will return 0, deactivate idle iocg or delete iocg
will set its inuse to zero correctly.
The inuse -> 1 happened in the test data turn out to be iocg_incur_debt(),
which call __propagate_weights() with active = weight, inuse = 0, so
clamp_t(u32, 0, 1, active) return 1.
Then this effect is very small, unlikely to have an impact in practice. Should
I modify the commit message to send v2 or just drop it?
Thanks.
> }
>
> iocg->last_inuse = iocg->inuse;
