[PATCH 06/12] fcoe: Round-robin based selection of CPU for post-processing of incoming commands

Robert Love
2011-06-20T23:30:40Z

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: Kiran Patil <kiran.patil@intel.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
---
drivers/scsi/fcoe/fcoe.c | 39 ++++++++++++++++++++++++++++++++++++++-
1 files changed, 38 insertions(+), 1 deletions(-)

diff --git a/drivers/scsi/fcoe/fcoe.c b/drivers/scsi/fcoe/fcoe.c
index 6378c58..da73115 100644
--- a/drivers/scsi/fcoe/fcoe.c
+++ b/drivers/scsi/fcoe/fcoe.c
@@ -1245,6 +1245,36 @@ static int fcoe_cpu_callback(struct notifier_block *nfb,
}

/**
+ * 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
* @netdev: The net device that the packet was received on
@@ -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)) {