Commit 064287ee authored by Kiran Patil's avatar Kiran Patil Committed by James Bottomley
Browse files

[SCSI] fcoe: Round-robin based selection of CPU for post-processing of incoming commands 



Problem: Earlier mechanism of selection of CPU was, to select the same CPU
which has received incoming request. Hence in case of rx_id = 0xFFFF,
request was always posted to same NetRx queue, hence only 1 CPU is utilized
for handling the command. It was also causing problem of "running out of
exchanges from per CPU pool of exchanges (in case of DDP offload)

Fix: Implemented new algo. to select CPU for post-processing of
incoming commands when rx_id is unknown. This is simple Round robin
algo. for CPU selection.

Notes/Dependencies: N/A

Signed-off-by: default avatarKiran Patil <kiran.patil@intel.com>
Signed-off-by: default avatarRobert Love <robert.w.love@intel.com>
Signed-off-by: default avatarJames Bottomley <JBottomley@Parallels.com>
parent 1ff9918b

drivers/scsi/fcoe/fcoe.c

+38 −1
Original line number Diff line number Diff line
@@ -1244,6 +1244,36 @@ static int fcoe_cpu_callback(struct notifier_block *nfb, 
	return NOTIFY_OK;

}



/**

 * fcoe_select_cpu() - Selects CPU to handle post-processing of incoming

 *			command.

 * @curr_cpu:   CPU which received request

 *

 * This routine selects next CPU based on cpumask.

 *

 * Returns: int (CPU number). Caller to verify if returned CPU is online or not.

 */

static unsigned int fcoe_select_cpu(unsigned int curr_cpu)

{

	static unsigned int selected_cpu;



	if (num_online_cpus() == 1)

		return curr_cpu;

	/*

	 * Doing following check, to skip "curr_cpu (smp_processor_id)"

	 * from selection of CPU is intentional. This is to avoid same CPU

	 * doing post-processing of command. "curr_cpu" to just receive

	 * incoming request in case where rx_id is UNKNOWN and all other

	 * CPU to actually process the command(s)

	 */

	do {

		selected_cpu = cpumask_next(selected_cpu, cpu_online_mask);

		if (selected_cpu >= nr_cpu_ids)

			selected_cpu = cpumask_first(cpu_online_mask);

	} while (selected_cpu == curr_cpu);

	return selected_cpu;

}



/**

 * fcoe_rcv() - Receive packets from a net device

 * @skb:    The received packet
@@ -1320,9 +1350,16 @@ int fcoe_rcv(struct sk_buff *skb, struct net_device *netdev, 
	 */

	if (ntoh24(fh->fh_f_ctl) & FC_FC_EX_CTX)

		cpu = ntohs(fh->fh_ox_id) & fc_cpu_mask;

	else

	else {

		cpu = smp_processor_id();



		if ((fh->fh_type == FC_TYPE_FCP) &&

		    (ntohs(fh->fh_rx_id) == FC_XID_UNKNOWN)) {

			do {

				cpu = fcoe_select_cpu(cpu);

			} while (!cpu_online(cpu));

		}

	}

	fps = &per_cpu(fcoe_percpu, cpu);

	spin_lock_bh(&fps->fcoe_rx_list.lock);

	if (unlikely(!fps->thread)) {

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