Subject: Re: [PATCH 1/6] bna: Brocade 10Gb Ethernet device driver

From: Stephen Hemminger <[email-masked]>
Date: Mon, 9 Aug 2010 11:15:05 -0400

On Fri, 6 Aug 2010 20:23:21 -0700
Debashis Dutt <[email-masked]> wrote:

> 
> Hi Stephen, 
> 
> Thanks a lot for your comments. 
> 
> > +                   if (likely
> > +                       (wis > BNA_QE_FREE_CNT(tcb, tcb->q_depth) ||
> > +                        vectors > BNA_QE_FREE_CNT(unmap_q, unmap_q->q_depth))) {
> > +                               BNAD_UPDATE_CTR(bnad, netif_queue_stop);
> > +                               return NETDEV_TX_BUSY;
> 
> >The transmit routine should check for available space after
> > queueing to device, so you can avoid having to return
> >TX_BUSY.
> 
> However your above comment is not very clear to me.
> 
> Our Tx routine already cleans up the Tx buffers at the end, through a tasklet.
> 
> Cleaning of Tx buffers happens 
> 1) In the sending context at the end of the Tx routine.
> 2) In the IRQ context when we get a Tx completion interrupt.
> 
> Only thing that we could have done, is do this check again at the end of the Tx routine
> and called netif_stop_queue() if required, so that the stack stops sending. Even then I am 
> not sure that we could avoid the current check and returning TX_BUSY.
> 
> It would be nice if you clarify, so that I understand this better.
> 
> Thanks
> --Debashis
> Linux LL Driver Team.
> 
> 
> -----Original Message-----
> From: Stephen Hemminger [mailto:[email-masked]] 
> Sent: Wednesday, August 04, 2010 10:09 AM
> To: Rasesh Mody
> Cc: [email-masked]; Debashis Dutt; Jing Huang
> Subject: Re: [PATCH 1/6] bna: Brocade 10Gb Ethernet device driver
> 
> On Tue, 3 Aug 2010 22:15:36 -0700
> Rasesh Mody <[email-masked]> wrote:
> 
> > From: Rasesh Mody <[email-masked]>
> > 
> > This is patch 1/6 which contains linux driver source for
> > Brocade's BR1010/BR1020 10Gb CEE capable ethernet adapter.
> > Source is based against net-next-2.6.
> > 
> > We wish this patch to be considered for inclusion in net-next-2.6
> > 
> > Signed-off-by: Rasesh Mody <[email-masked]>
> > ---
> >  bnad.c         | 3326 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  bnad.h         |  474 ++++++++
> >  bnad_ethtool.c | 1269 +++++++++++++++++++++
> >  3 files changed, 5069 insertions(+)
> > 
> > diff -ruP net-next-2.6.35-rc1-orig/drivers/net/bna/bnad.c net-next-2.6.35-rc1-mod/drivers/net/bna/bnad.c
> > --- net-next-2.6.35-rc1-orig/drivers/net/bna/bnad.c         1969-12-31 16:00:00.000000000 -0800
> > +++ net-next-2.6.35-rc1-mod/drivers/net/bna/bnad.c     2010-08-02 17:19:19.447239000 -0700
> > @@ -0,0 +1,3326 @@
> > +/*
> > + * Linux network driver for Brocade Converged Network Adapter.
> > + *
> > + * This program is free software; you can redistribute it and/or modify it
> > + * under the terms of the GNU General Public License (GPL) Version 2 as
> > + * published by the Free Software Foundation
> > + *
> > + * This program is distributed in the hope that it will be useful, but
> > + * WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > + * General Public License for more details.
> > + */
> > +/*
> > + * Copyright (c) 2005-2009 Brocade Communications Systems, Inc.
> > + * All rights reserved
> > + * www.brocade.com
> > + */
> > +#include <linux/netdevice.h>
> > +#include <linux/skbuff.h>
> > +#include <linux/etherdevice.h>
> > +#include <linux/in.h>
> > +#include <linux/ethtool.h>
> > +#include <linux/if_vlan.h>
> > +#include <linux/if_ether.h>
> > +#include <linux/ip.h>
> > +
> > +#include "bnad.h"
> > +#include "bna.h"
> > +#include "cna.h"
> > +
> > +DEFINE_MUTEX(bnad_fwimg_mutex);
> > +
> > +/*
> > + * Module params
> > + */
> > +static uint bnad_msix_disable;
> > +module_param(bnad_msix_disable, uint, 0444);
> > +MODULE_PARM_DESC(bnad_msix_disable, "Disable MSIX mode");
> > +
> > +static uint bnad_ioc_auto_recover = 1;
> > +module_param(bnad_ioc_auto_recover, uint, 0444);
> > +MODULE_PARM_DESC(bnad_ioc_auto_recover, "Enable / Disable auto recovery");
> > +
> > +/*
> > + * Global variables
> > + */
> > +u32 bna_id;
> > +u32 bnad_rxqs_per_cq = 2;
> > +
> > +DECLARE_MUTEX(bnad_list_sem);
> > +LIST_HEAD(bnad_list);
> > +
> > +const u8 bnad_bcast_addr[] =  {0xff, 0xff, 0xff, 0xff, 0xff, 0xff};
> 
> Surprised this isn't defined somewhere else.
> 
> > +
> > +/*
> > + * Local MACROS
> > + */
> > +#define BNAD_TX_UNMAPQ_DEPTH (bnad->txq_depth * 2)
> > +
> > +#define BNAD_RX_UNMAPQ_DEPTH (bnad->rxq_depth)
> > +
> > +#define BNAD_GET_MBOX_IRQ(_bnad)                                            \
> > +       (((_bnad)->cfg_flags & BNAD_CF_MSIX) ?                                 \
> > +       ((_bnad)->msix_table[(_bnad)->msix_num - 1].vector) :   \
> > +       ((_bnad)->pcidev->irq))
> > +
> > +#define BNAD_FILL_UNMAPQ_MEM_REQ(_res_info, _num, _depth)  \
> > +do {                                                                                     \
> > +       (_res_info)->res_type = BNA_RES_T_MEM;                               \
> > +       (_res_info)->res_u.mem_info.mem_type = BNA_MEM_T_KVA;    \
> > +       (_res_info)->res_u.mem_info.num = (_num);                   \
> > +       (_res_info)->res_u.mem_info.len =                                 \
> > +       sizeof(struct bnad_unmap_q) +                                      \
> > +       (sizeof(struct bnad_skb_unmap) * ((_depth) - 1));            \
> > +} while (0)
> > +
> > +void
> > +bnad_add_to_list(struct bnad *bnad)
> > +{
> > +       down(&bnad_list_sem);
> > +       list_add_tail(&bnad->list_entry, &bnad_list);
> > +       bna_id++;
> > +       up(&bnad_list_sem);
> > +}
> 
> Why do you need to list semaphore? Isn't RTNL mutex held
> when this is done. If you have to have own exclusion use
> a mutex for this.
> 
> > +void
> > +bnad_remove_from_list(struct bnad *bnad)
> > +{
> > +       down(&bnad_list_sem);
> > +       list_del(&bnad->list_entry);
> > +       up(&bnad_list_sem);
> > +}
> > +
> > +const struct pci_device_id bnad_pci_id_table[] = {
> > +       {
> > +                   PCI_DEVICE(PCI_VENDOR_ID_BROCADE,
> > +                               PCI_DEVICE_ID_BROCADE_CT),
> > +                   .class = PCI_CLASS_NETWORK_ETHERNET << 8,
> > +                   .class_mask =  0xffff00
> > +       }, {0,  }
> > +};
> 
> Why is this not static?
> 
> 
> > +/* TX */
> > +/* bnad_start_xmit : Netdev entry point for Transmit */
> > +/*                      Called under lock held by net_device */
> > +
> > +netdev_tx_t
> > +bnad_start_xmit(struct sk_buff *skb, struct net_device *netdev)
> 
> Should also be static...
> 
> > +{
> > +       struct bnad *bnad = netdev_priv(netdev);
> > +
> > +       u16                   txq_prod, vlan_tag = 0;
> > +       u32                   unmap_prod, wis, wis_used, wi_range;
> > +       u32                   vectors, vect_id, i, acked;
> > +       u32                   tx_id;
> > +       int                                 err;
> > +
> > +       struct bnad_tx_info *tx_info;
> > +       struct bna_tcb *tcb;
> > +       struct bnad_unmap_q *unmap_q;
> > +       dma_addr_t                  dma_addr;
> > +       struct bna_txq_entry *txqent;
> > +       bna_txq_wi_ctrl_flag_t   flags;
> > +
> > +       if (unlikely
> > +           (skb->len <= ETH_HLEN || skb->len > BFI_TX_MAX_DATA_PER_PKT)) {
> > +                   dev_kfree_skb(skb);
> > +                   return NETDEV_TX_OK;
> > +       }
> > +
> > +       /*
> > +       * Takes care of the Tx that is scheduled between clearing the flag
> > +       * and the netif_stop_queue() call.
> > +       */
> > +       if (unlikely(!test_bit(BNAD_RF_TX_STARTED, &bnad->run_flags))) {
> > +                   dev_kfree_skb(skb);
> > +                   return NETDEV_TX_OK;
> > +       }
> > +
> > +       tx_id = BNAD_GET_TX_ID(skb);
> > +
> > +       tx_info = &bnad->tx_info[tx_id];
> > +       tcb = tx_info->tcb[tx_id];
> > +       unmap_q = tcb->unmap_q;
> > +
> > +       vectors = 1 + skb_shinfo(skb)->nr_frags;
> > +       if (vectors > BFI_TX_MAX_VECTORS_PER_PKT) {
> > +                   dev_kfree_skb(skb);
> > +                   return NETDEV_TX_OK;
> > +       }
> > +       wis = BNA_TXQ_WI_NEEDED(vectors); /* 4 vectors per work item */
> > +       acked = 0;
> > +       if (unlikely
> > +           (wis > BNA_QE_FREE_CNT(tcb, tcb->q_depth) ||
> > +            vectors > BNA_QE_FREE_CNT(unmap_q, unmap_q->q_depth))) {
> > +                   if ((u16) (*tcb->hw_consumer_index) !=
> > +                       tcb->consumer_index &&
> > +                       !test_and_set_bit(BNAD_TXQ_FREE_SENT, &tcb->flags)) {
> > +                               acked = bnad_free_txbufs(bnad, tcb);
> > +                               bna_ib_ack(tcb->i_dbell, acked);
> > +                               smp_mb__before_clear_bit();
> > +                               clear_bit(BNAD_TXQ_FREE_SENT, &tcb->flags);
> > +                   } else {
> > +                               netif_stop_queue(netdev);
> > +                               BNAD_UPDATE_CTR(bnad, netif_queue_stop);
> > +                   }
> > +
> > +                   smp_mb();
> > +                   /*
> > +                   * Check again to deal with race condition between
> > +                   * netif_stop_queue here, and netif_wake_queue in
> > +                   * interrupt handler which is not inside netif tx lock.
> > +                   */
> > +                   if (likely
> > +                       (wis > BNA_QE_FREE_CNT(tcb, tcb->q_depth) ||
> > +                        vectors > BNA_QE_FREE_CNT(unmap_q, unmap_q->q_depth))) {
> > +                               BNAD_UPDATE_CTR(bnad, netif_queue_stop);
> > +                               return NETDEV_TX_BUSY;
> 
> The transmit routine should check for available space after
> queueing to device, so you can avoid having to return
> TX_BUSY.

The problem is that if device returns TX_BUSY, the net transmit scheduler
will end up re-calling the transmit routine.  This looks ok in your driver
because it will set netif_stop_queue