[PATCH] 3/5 ibmveth fix buffer replenishing

[Santiago Leon <santil@us.ibm.com>]

This patch removes the allocation of RX skb's  buffers from a workqueue
to be called directly at RX processing time.  This change was suggested
by Dave Miller when the driver was starving the RX buffers and
deadlocking under heavy traffic:

> Allocating RX SKBs via tasklet is, IMHO, the worst way to
> do it.  It is no surprise that there are starvation cases.
> 
> If tasklets or work queues get delayed in any way, you lose,
> and it's very easy for a card to catch up with the driver RX'ing
> packets very fast, no matter how aggressive you make the
> replenishing.  By the time you detect that you need to be
> "more aggressive" it is already too late.
> The only pseudo-reliable way is to allocate at RX processing time.
> 

Signed-off-by: Santiago Leon <santil@us.ibm.com>
---
drivers/net/ibmveth.c |   48
++++++++----------------------------------------
drivers/net/ibmveth.h |    4 ----
2 files changed, 8 insertions(+), 44 deletions(-)
---
diff -urN a/drivers/net/ibmveth.c b/drivers/net/ibmveth.c
--- a/drivers/net/ibmveth.c 2005-10-17 12:04:58.000000000 -0500
+++ b/drivers/net/ibmveth.c 2005-10-17 12:23:22.000000000 -0500
@@ -96,7 +96,6 @@
static void ibmveth_proc_register_adapter(struct ibmveth_adapter
*adapter);
static void ibmveth_proc_unregister_adapter(struct ibmveth_adapter
*adapter);
static irqreturn_t ibmveth_interrupt(int irq, void *dev_instance, struct
pt_regs *regs);
-static inline void ibmveth_schedule_replenishing(struct
ibmveth_adapter*);
static inline void ibmveth_rxq_harvest_buffer(struct ibmveth_adapter
*adapter);

#ifdef CONFIG_PROC_FS
@@ -257,29 +256,7 @@
atomic_add(buffers_added, &(pool->available));
}

-/* check if replenishing is needed.  */
-static inline int ibmveth_is_replenishing_needed(struct ibmveth_adapter
*adapter)
-{
- int i;
-
- for(i = 0; i < IbmVethNumBufferPools; i++)
- if(adapter->rx_buff_pool[i].active &&
-   (atomic_read(&adapter->rx_buff_pool[i].available) <
-    adapter->rx_buff_pool[i].threshold))
- return 1;
- return 0;
-}
-
-/* kick the replenish tasklet if we need replenishing and it isn't
already running */
-static inline void ibmveth_schedule_replenishing(struct ibmveth_adapter
*adapter)
-{
- if(ibmveth_is_replenishing_needed(adapter) &&
-    (atomic_dec_if_positive(&adapter->not_replenishing) == 0)) {
- schedule_work(&adapter->replenish_task);
- }
-}
-
-/* replenish tasklet routine */
+/* replenish routine */
static void ibmveth_replenish_task(struct ibmveth_adapter *adapter) 
{
int i;
@@ -292,10 +269,6 @@
     &adapter->rx_buff_pool[i]);

adapter->rx_no_buffer = *(u64*)(((char*)adapter->buffer_list_addr) +
4096 - 8);
-
- atomic_inc(&adapter->not_replenishing);
-
- ibmveth_schedule_replenishing(adapter);
}

/* empty and free ana buffer pool - also used to do cleanup in error
paths */
@@ -563,10 +536,10 @@
return rc;
}

- netif_start_queue(netdev);
+ ibmveth_debug_printk("initial replenish cycle\n");
+ ibmveth_replenish_task(adapter);

- ibmveth_debug_printk("scheduling initial replenish cycle\n");
- ibmveth_schedule_replenishing(adapter);
+ netif_start_queue(netdev);

ibmveth_debug_printk("open complete\n");

@@ -584,9 +557,6 @@

free_irq(netdev->irq, netdev);

- cancel_delayed_work(&adapter->replenish_task);
- flush_scheduled_work();
-
do {
lpar_rc = h_free_logical_lan(adapter->vdev->unit_address);
} while (H_isLongBusy(lpar_rc) || (lpar_rc == H_Busy));
@@ -795,7 +765,7 @@
}
} while(more_work && (frames_processed < max_frames_to_process));

- ibmveth_schedule_replenishing(adapter);
+ ibmveth_replenish_task(adapter);

if(more_work) {
/* more work to do - return that we are not done yet */
@@ -931,8 +901,10 @@

}

+ /* kick the interrupt handler so that the new buffer pools get
+    replenished or deallocated */
+ ibmveth_interrupt(dev->irq, dev, NULL);

- ibmveth_schedule_replenishing(adapter);
dev->mtu = new_mtu;
return 0; 
}
@@ -1017,14 +989,10 @@

ibmveth_debug_printk("adapter @ 0x%p\n", adapter);

- INIT_WORK(&adapter->replenish_task, (void*)ibmveth_replenish_task,
(void*)adapter);
-
adapter->buffer_list_dma = DMA_ERROR_CODE;
adapter->filter_list_dma = DMA_ERROR_CODE;
adapter->rx_queue.queue_dma = DMA_ERROR_CODE;

- atomic_set(&adapter->not_replenishing, 1);
-
ibmveth_debug_printk("registering netdev...\n");

rc = register_netdev(netdev);
diff -urN a/drivers/net/ibmveth.h b/drivers/net/ibmveth.h
--- a/drivers/net/ibmveth.h 2005-10-17 12:04:58.000000000 -0500
+++ b/drivers/net/ibmveth.h 2005-10-17 12:23:22.000000000 -0500
@@ -118,10 +118,6 @@
     dma_addr_t filter_list_dma;
     struct ibmveth_buff_pool rx_buff_pool[IbmVethNumBufferPools];
     struct ibmveth_rx_q rx_queue;
-    atomic_t not_replenishing;
-
-    /* helper tasks */
-    struct work_struct replenish_task;

     /* adapter specific stats */
     u64 replenish_task_cycles;

-- 
Santiago A. Leon
Power Linux Development
IBM Linux Technology Center