Re: [PATCH 11/13] target: replace work per cmd in completion path

On Tue, Feb 09, 2021 at 06:38:43AM -0600, Mike Christie wrote:

Doing a work per cmd can lead to lots of threads being created.
This patch just replaces the completion work per cmd with a per cpu
list. Combined with the first patches this allows tcm loop on top of
initiators like iser to go from around 700K IOPs to 1000K and reduces
the number of threads that get created when the system is under heavy
load and hitting the initiator drivers tagging limits.

OTOH it does increase completion latency, which might be the preference
for some workloads.  Do we need a tunable here?

+static void target_queue_cmd_work(struct se_cmd_queue *q, struct se_cmd *se_cmd,
+				  int cpu, struct workqueue_struct *wq)
 {
-	struct se_cmd *cmd = container_of(work, struct se_cmd, work);
+	llist_add(&se_cmd->se_cmd_list, &q->cmd_list);
+	queue_work_on(cpu, wq, &q->work);
+}

Do we need this helper at all?  Having it open coded in the two callers
would seem easier to follow to me.

_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization