Andi Kleen wrote:
On Tue, Dec 09, 2008 at 03:10:17PM -0800, Robert Love wrote:
libFC is composed of 4 blocks supported by an exchange manager
and a framing library. The upper 4 layers are fc_lport, fc_disc,
fc_rport and fc_fcp. A LLD that uses libfc could choose to
either use libfc's block, or using the transport template
defined in libfc.h, override one or more blocks with its own
implementation.
Just some more stuff I noticed while looking briefly at libfcoe.c
Not a complete review again.
230 #ifdef CONFIG_SMP
231 /*
232 * The exchange ID are ANDed with num of online CPUs,
233 * so that will have the least lock contention in
234 * handling the exchange. if there is no thread
235 * for a given idx then use first online cpu.
236 */
237 cpu_idx = oxid & (num_online_cpus() >> 1);
238 if (fcoe_percpu[cpu_idx] == NULL)
239 cpu_idx = first_cpu(cpu_online_map);
240 #endif
What is this supposed to do? It looks quite dubious.
It had load balancing issue but now it is fixed, related latest
submitted code with its updated comment is:-
/*
* The incoming frame exchange id(oxid) is ANDed with num of online
* cpu bits to get cpu_idx and then this cpu_idx is used for selecting
* a per cpu kernel thread from fcoe_percpu. In case the cpu is
* offline or no kernel thread for derived cpu_idx then cpu_idx is
* initialize to first online cpu index.
*/
cpu_idx = oxid & (num_online_cpus() - 1);
if (!fcoe_percpu[cpu_idx] || !cpu_online(cpu_idx))
cpu_idx = first_cpu(cpu_online_map);
The incoming FC frame is distributed across all fcoe_percpu_receive_thread for better load balancing, these per CPU threads are created by fcoe module during fcoe_init. This should help in performance but not sure how much since performance tuning is yet to be done.
Shouldn't this use the current CPU number?
The current cpu could be used here with some other ingress FC frames
distribution/hashing across all cpus instead this hash logic "oxid &
(num_online_cpus() - 1)", possibly ingress FC frame distribution at soft
irq level by oxid and then passing up to current cpu's kernel thread
fcoe_percpu_receive_thread.
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