Re: [dpdk-dev] [PATCH] event/opdl: fix atomic queue race condition issue

["Van Haaren, Harry" <harry.van.haaren@intel.com>]

> From: Ma, Liang J
> Sent: Tuesday, March 13, 2018 11:34 AM
> To: jerin.jacob@caviumnetworks.com
> Cc: dev@dpdk.org; Van Haaren, Harry <harry.van.haaren@intel.com>; Jain, Deepak
> K <deepak.k.jain@intel.com>; Geary, John <john.geary@intel.com>; Mccarthy,
> Peter <peter.mccarthy@intel.com>
> Subject: [PATCH] event/opdl: fix atomic queue race condition issue
> 
> If application link one atomic queue to multiple ports,
> and each worker core update flow_id, there will have a
> chance to hit race condition issue and lead to double processing
> same event. This fix solve the problem and eliminate
> the race condition issue.
> 
> Fixes: 4236ce9bf5bf ("event/opdl: add OPDL ring infrastructure library")
> 

General notes
- Spaces around & % << >> and other bitwise manipulations (https://dpdk.org/doc/guides/contributing/coding_style.html#operators)
- I've noted a few below, but there are more
- Usually checkpatch flags these - I'm curious why it didn't in this case

It would be nice if we didn't have to rely on __atomic_load_n() and friends,
however I don't see a better alternative. Given other DPDK components are
also using __atomic_* functions, no objection here.


<snip>

> @@ -520,7 +528,17 @@ opdl_stage_claim_singlethread(struct opdl_stage *s, void
> *entries,
> 
>  		for (j = 0; j < num_entries; j++) {
>  			ev = (struct rte_event *)get_slot(t, s->head+j);
> -			if ((ev->flow_id%s->nb_instance) == s->instance_id) {

Spaces around the %

> +
> +			event  = __atomic_load_n(&(ev->event),
> +					__ATOMIC_ACQUIRE);
> +
> +			opa_id = OPDL_OPA_MASK&(event>>OPDL_OPA_OFFSET);

Spaces &

> +			flow_id  = OPDL_FLOWID_MASK&event;

Spaces &

> +
> +			if (opa_id >= s->queue_id)
> +				continue;
> +
> +			if ((flow_id%s->nb_instance) == s->instance_id) {

Spaces %

<snip rest of patch>


Will re-review v2. Cheers, -Harry