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

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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>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
This commit is contained in:
Kiran Patil 2011-06-20 16:59:20 -07:00 committed by James Bottomley
parent 1ff9918b62
commit 064287eee3
1 changed files with 38 additions and 1 deletions
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39
drivers/scsi/fcoe/fcoe.c
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@ -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)) {