hi all: I think I got it. The new kernel just remove the NIC from poll list first, If we should repoll it, kernel will add it again. The codes is: 4560 static void net_rx_action(struct softirq_action *h) 4561 { 4562 struct softnet_data *sd = this_cpu_ptr(&softnet_data); 4563 unsigned long time_limit = jiffies + 2; 4564 int budget = netdev_budget; 4565 LIST_HEAD(list); 4566 LIST_HEAD(repoll); 4567 void *have; 4568 4569 local_irq_disable(); 4570 list_splice_init(&sd->poll_list, &list); 4571 local_irq_enable(); 4572 4573 while (!list_empty(&list)) { 4574 struct napi_struct *n; 4575 int work, weight; 4576 4577 /* If softirq window is exhausted then punt. 4578 * Allow this to run for 2 jiffies since which will allow 4579 * an average latency of 1.5/HZ. 4580 */ 4581 if (unlikely(budget <= 0 || time_after_eq(jiffies, time_limit))) 4582 goto softnet_break; 4583 4584 4585 n = list_first_entry(&list, struct napi_struct, poll_list); 4586 list_del_init(&n->poll_list); 4587 4588 have = netpoll_poll_lock(n); 4589 4590 weight = n->weight; 4591 4592 /* This NAPI_STATE_SCHED test is for avoiding a race 4593 * with netpoll's poll_napi(). Only the entity which 4594 * obtains the lock and sees NAPI_STATE_SCHED set will 4595 * actually make the ->poll() call. Therefore we avoid 4596 * accidentally calling ->poll() when NAPI is not scheduled. 4597 */ 4598 work = 0; 4599 if (test_bit(NAPI_STATE_SCHED, &n->state)) { 4600 work = n->poll(n, weight); 4601 trace_napi_poll(n); 4602 } 4603 4604 WARN_ON_ONCE(work > weight); 4605 4606 budget -= work; 4607 4608 /* Drivers must not modify the NAPI state if they 4609 * consume the entire weight. In such cases this code 4610 * still "owns" the NAPI instance and therefore can 4611 * move the instance around on the list at-will. 4612 */ 4613 if (unlikely(work == weight)) { 4614 if (unlikely(napi_disable_pending(n))) { 4615 napi_complete(n); 4616 } else { 4617 if (n->gro_list) { 4618 /* flush too old packets 4619 * If HZ < 1000, flush all packets. 4620 */ 4621 napi_gro_flush(n, HZ >= 1000); 4622 } 4623 list_add_tail(&n->poll_list, &repoll); 4624 } 4625 } 4626 4627 netpoll_poll_unlock(have); 4628 } 4629 4630 if (!sd_has_rps_ipi_waiting(sd) && 4631 list_empty(&list) && 4632 list_empty(&repoll)) 4633 return; 4634 out: 4635 local_irq_disable(); 4636 4637 list_splice_tail_init(&sd->poll_list, &list); 4638 list_splice_tail(&repoll, &list); 4639 list_splice(&list, &sd->poll_list); 4640 if (!list_empty(&sd->poll_list)) 4641 __raise_softirq_irqoff(NET_RX_SOFTIRQ); 4642 4643 net_rps_action_and_irq_enable(sd); 4644 4645 return; 4646 4647 softnet_break: 4648 sd->time_squeeze++; 4649 goto out; 4650 } line 4585: choose a NIC which will poll. line 4586: remove the NIC from the poll list. line 4623: add the NIC again in repoll list if we nedd poll it. line 4638: splice the poll list and repoll list. So, I think this is not a bug. @valdis.kletnieks I think we should remove NIC form poll list after the list of sd->input_pkt_queue is empty, so I think code should run like this: 4350 rps_lock(sd); 4351 if (skb_queue_empty(&sd->input_pkt_queue)) { 4352 /* 4353 * Inline a custom version of __napi_complete(). 4354 * only current cpu owns and manipulates this napi, 4355 * and NAPI_STATE_SCHED is the only possible flag set 4356 * on backlog. 4357 * We can use a plain write instead of clear_bit(), 4358 * and we dont need an smp_mb() memory barrier. 4359 */ list_del(&napi->poll_list); // I add it. 4360 napi->state = 0; 4361 rps_unlock(sd); 4362 4363 break; 4364 } Thank you 在 2014/12/23 20:13, Vignesh Radhakrishnan 写道:

We do delete it. I am not very thorough with the code , but here is what i think is happening.

process_backlog is set as the backlog polling function for softnet data sd->backlog.poll = process_backlog;

Now net_rx_action which runs in soft irq context, calls the polling as per the following code and the deletion as well.

Notice where we are deleting it :

n = list_first_entry(&list, struct napi_struct, poll_list); list_del_init(&n->poll_list); --------------------------------------> Here is the deletion.

have = netpoll_poll_lock(n);

weight = n->weight;

/* This NAPI_STATE_SCHED test is for avoiding a race * with netpoll's poll_napi(). Only the entity which * obtains the lock and sees NAPI_STATE_SCHED set will * actually make the ->poll() call. Therefore we avoid * accidentally calling ->poll() when NAPI is not scheduled. */ work = 0; if (test_bit(NAPI_STATE_SCHED, &n->state)) { work = n->poll(n, weight); -------------------------------------> Process_backlog is called here trace_napi_poll(n); }

Earlier we had deletion in process_backlog itself, but https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=d... has changed it.

Thanks and regards, Vignesh Radhakrishnan

On Tue, Dec 23, 2014 at 2:29 PM, lx <lxlenovostar@gmail.com <mailto:lxlenovostar@gmail.com>> wrote:

hi all: I read the function of process_backlog, and I found it don't delete the NIC form poll list. the codes is:

4321 static int process_backlog(struct napi_struct *napi, int quota) 4322 { 4323 int work = 0; 4324 struct softnet_data *sd = container_of(napi, struct softnet_data, backlog); 4325 4326 /* Check if we have pending ipi, its better to send them now, 4327 * not waiting net_rx_action() end. 4328 */ 4329 if (sd_has_rps_ipi_waiting(sd)) { 4330 local_irq_disable(); 4331 net_rps_action_and_irq_enable(sd); 4332 } 4333 4334 napi->weight = weight_p; 4335 local_irq_disable(); 4336 while (1) { 4337 struct sk_buff *skb; 4338 4339 while ((skb = __skb_dequeue(&sd->process_queue))) { 4340 local_irq_enable(); 4341 __netif_receive_skb(skb); 4342 local_irq_disable(); 4343 input_queue_head_incr(sd); 4344 if (++work >= quota) { 4345 local_irq_enable(); 4346 return work; 4347 } 4348 } 4349 4350 rps_lock(sd); 4351 if (skb_queue_empty(&sd->input_pkt_queue)) { 4352 /* 4353 * Inline a custom version of __napi_complete(). 4354 * only current cpu owns and manipulates this napi, 4355 * and NAPI_STATE_SCHED is the only possible flag set 4356 * on backlog. 4357 * We can use a plain write instead of clear_bit(), 4358 * and we dont need an smp_mb() memory barrier. 4359 */ 4360 napi->state = 0; 4361 rps_unlock(sd); 4362 4363 break; 4364 } 4365 4366 skb_queue_splice_tail_init(&sd->input_pkt_queue, 4367 &sd->process_queue); 4368 rps_unlock(sd); 4369 } 4370 local_irq_enable(); 4371 4372 return work; 4373 }

I think we should delete the NIC from the poll list by: list_del(&napi->poll_list);

and my git repository infromation is:

[root@localhost linux]# git show commit aa39477b5692611b91ac9455ae588738852b3f60 Merge: 48ec833 5164bec Author: Linus Torvalds <torvalds@linux-foundation.org <mailto:torvalds@linux-foundation.org>> Date: Mon Dec 22 14:47:17 2014 -0800

Merge tag 'dm-3.19-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm <http://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm> Pull device mapper fixes from Mike Snitzer: "Thre stable fixes and one fix for a regression introduced during 3.19 merge: - Fix inability to discard used space when the thin-pool target is in out-of-data-space mode and also transition the thin-pool back to write mode once free space is made available. - Fix DM core bio-based end_io bug that prevented proper post-processing of the error code returned from the block layer. - Fix crash in DM thin-pool due to thin device being added to the pool's active_thins list before properly initializing the thin device's refcount" * tag 'dm-3.19-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm <http://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm>: dm: fix missed error code if .end_io isn't implemented by target_type dm thin: fix crash by initializing thin device's refcount and completion earlier dm thin: fix missing out-of-data-space to write mode transition if blocks are released dm thin: fix inability to discard blocks when in out-of-data-space mode

Don't handle the list_del is right, or this is a bug?

Thank you.

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