On 5/26/21 8:48 PM, Damien Le Moal wrote:
> On 2021/05/27 10:02, Bart Van Assche wrote:
>> + if (next->elv.priv[0]) {
>> + atomic_inc(&dd->merged[prio]);
>> + } else {
>> + WARN_ON_ONCE(true);
>> + }
>
> I do not think you need the curly braces here.
These are present because patch 9/9 adds more code in this if-statement
and to improve readability of patch 9/9.
>> @@ -392,9 +453,14 @@ static struct request *dd_dispatch_request(struct blk_mq_hw_ctx *hctx)
>> {
>> struct deadline_data *dd = hctx->queue->elevator->elevator_data;
>> struct request *rq;
>> + enum dd_prio prio;
>>
>> spin_lock(&dd->lock);
>> - rq = __dd_dispatch_request(dd);
>> + for (prio = 0; prio <= DD_PRIO_MAX; prio++) {
>> + rq = __dd_dispatch_request(dd, prio);
>> + if (rq || dd_queued(dd, prio))
>> + break;
>> + }
>> spin_unlock(&dd->lock);
>
> Unless I missed something, this means that the aging (fifo list expire)
> mechanism is per prio list but there is no aging between the prio classes. This
> means that an application doing lots of RT direct IOs will completely starve
> other prio classes and hang the applications using them.
>
> I think we need aging between the prio classes too to avoid that.
OK, I will add an aging mechanism.
Bart.
