Date:	Thu, 20 Jun 2013 19:46:58 +0000
From:	"Nelson, Shannon" <shannon.nelson@...el.com>
To:	Ben Hutchings <bhutchings@...arflare.com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"gospo@...hat.com" <gospo@...hat.com>,
	"sassmann@...hat.com" <sassmann@...hat.com>,
	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>,
	"e1000-devel@...ts.sourceforge.net" 
	<e1000-devel@...ts.sourceforge.net>
Subject: RE: [net-next 1/8] i40e: main driver core

> From: Ben Hutchings [mailto:bhutchings@...arflare.com]
> Sent: Wednesday, June 19, 2013 11:13 AM
> 
> On Thu, 2013-06-13 at 20:55 -0700, Jeff Kirsher wrote:
> > From: Jesse Brandeburg <jesse.brandeburg@...el.com>
> >
> > This is the driver for the Intel(R) Ethernet Controller XL710 Family.
> >
> > This driver is targeted at basic ethernet functionality only, and will
> be
> > improved upon further as time goes on.
> >
> > This patch mail contains the driver entry points but does not include
> transmit
> > and receive (see next patch) routines.
> 
> Aside from the poor style of using your own private error names *even in
> netdev operations*, you're also not using consistent types for them
> (int, s32 or u32?).
> 
> [...]
> > --- /dev/null
> > +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
> [...]
> > +#define I40E_MAX_NIC 32
> 
> This doesn't appear to be used (thankfully).

Yep, we'll make it go away.

> 
> [...]
> > +void i40e_tx_timeout(struct net_device *netdev)
> > +{
> > +	struct i40e_netdev_priv *np = netdev_priv(netdev);
> > +	struct i40e_vsi *vsi = np->vsi;
> > +	struct i40e_pf *pf = vsi->back;
> > +
> > +	pf->tx_timeout_count++;
> > +#ifdef CONFIG_DEBUG_FS
> > +	if (vsi->block_tx_timeout) {
> > +		netdev_info(netdev, "%s: recovery disabled\n", __func__);
> > +		return;
> > +	}
> > +#endif
> 
> Looks like a development hack.

Well, validation hack, but yes it needs to get stripped.

> 
> > +	if (time_after(jiffies, (pf->tx_timeout_last_recovery + HZ*20)))
> > +		pf->tx_timeout_recovery_level = 0;
> > +	pf->tx_timeout_last_recovery = jiffies;
> > +	vsi->netdev->trans_start = jiffies;
> 
> Direct assignment of net_device::trans_start is deprecated, and
> definitely wrong for a multiqueue driver.

Yep.

> 
> [...]
> > +/**
> > + * i40e_get_vsi_stats_struct - Get System Network Statistics
> > + * @vsi: the VSI we care about
> > + *
> > + * Returns the address of the device statistics structure.
> > + * The statistics are actually updated from the service task.
> > + **/
> > +struct net_device_stats *i40e_get_vsi_stats_struct(struct i40e_vsi
> *vsi)
> > +{
> > +	/* only return the current stats */
> > +	/* It is possible for a VSIs to not have a netdev */
> > +	if (vsi->netdev)
> > +		return &vsi->netdev->stats;
> > +	else
> > +		return &vsi->net_stats;
> > +}
> 
> You should be using rtnl_device_stats64; at 40G a 32-bit counter is
> ridiculous (using this in a 32-bit machine is a bit ridiculous too,
> though...)

You mean rtnl_link_stats64?  Sure.

Yes, this driver is really not meant for a 32-bit machine.  We've discussed making sure it would only build for 64-bit, but hadn't quite gotten around to implementing the restriction.  It seems the right thing to do - would anyone in the community get bent out of shape if we added that?

> 
> [...]
> > +/**
> > + * i40e_vlan_rx_register - Setup or shutdown vlan offload
> > + * @netdev: network interface to be adjusted
> > + * @features: netdev features to test if VLAN offload is enabled or
> not
> > + **/
> > +static void i40e_vlan_rx_register(struct net_device *netdev, u32
> features)
> > +{
> > +	struct i40e_netdev_priv *np = netdev_priv(netdev);
> > +	struct i40e_vsi *vsi = np->vsi;
> > +	bool enable;
> > +	enable = !!(features & NETIF_F_HW_VLAN_CTAG_RX);
> > +
> > +	if (enable)
> 
> It's a simple expression; why bother with a variable for it?

Yep

> 
> > +		i40e_vlan_stripping_enable(vsi);
> > +	else
> > +		i40e_vlan_stripping_disable(vsi);
> > +}
> [...]
> > +/**
> > + * i40e_napi_disable_all - Disable NAPI for all q_vectors in the VSI
> > + * @vsi: the VSI being configured
> > + **/
> > +static void i40e_napi_disable_all(struct i40e_vsi *vsi)
> > +{
> > +	int q_idx;
> > +
> > +	if (!vsi->netdev)
> > +		return;
> > +
> > +	for (q_idx = 0; q_idx < vsi->num_q_vectors; q_idx++) {
> > +		napi_synchronize(&vsi->q_vectors[q_idx].napi);
> 
> This will wait indefinitely if there is enough traffic to keep NAPI
> scheduled.  (Arguably this is a bug in napi_synchronize() and it should
> actually use some sort of generation count.)  It's completely pointless
> when you're about to call:
> 
> > +		napi_disable(&vsi->q_vectors[q_idx].napi);
> 
> which will actually tell the NAPI soft IRQ to stop.

Makes sense.

> 
> > +	}
> > +}
> [...]
> > +/**
> > + * i40e_vsi_reinit_locked - Reset the VSI
> > + * @vsi: the VSI being configured
> > + *
> > + * Rebuild the ring structs after some configuration
> > + * has changed, e.g. MTU size.
> > + **/
> > +static void i40e_vsi_reinit_locked(struct i40e_vsi *vsi)
> > +{
> > +	struct i40e_pf *pf = vsi->back;
> > +
> > +	WARN_ON(in_interrupt());
> > +	/* put off any impending NetWatchDogTimeout */
> > +	if (vsi->netdev)
> > +		vsi->netdev->trans_start = jiffies;
> 
> Leave trans_start alone.

Got it.

> 
> [...]
> > +/**
> > + * i40e_down - Shutdown the connection processing
> > + * @vsi: the VSI being stopped
> > + **/
> > +void i40e_down(struct i40e_vsi *vsi)
> > +{
> > +	int i;
> > +
> > +	/* It is assumed that the caller of this function
> > +	 * sets the vsi->state __I40E_DOWN bit.
> > +	 */
> > +	if (vsi->netdev) {
> > +		netif_tx_stop_all_queues(vsi->netdev);
> > +		netif_carrier_off(vsi->netdev);
> > +		netif_tx_disable(vsi->netdev);
> 
> This seems very confused.  Do you want to stop TX synchronously or
> asynchronously?

We'll clean this up.

> 
> [...]
> > +/**
> > + * i40e_check_hang_subtask - Check for hung queues and dropped
> interrupts
> > + * @pf: board private structure
> > + *
> > + * Set the per-queue flags to request a check for stuck queues in the
> irq
> > + * clean functions, then force interrupts to be sure the irq clean is
> called.
> > + **/
> > +static void i40e_check_hang_subtask(struct i40e_pf *pf)
> > +{
> [...]
> 
> We already have a TX watchdog.

Yes, and it is effective.  However, as in the ixgbe code, we want to take the opportunity to check a couple other things and perhaps clean up a problem before it is noticed further up the stack, thus avoiding the more painful TX hang recovery if possible.

> 
> [...]
> > +/**
> > + * i40e_config_rss - Prepare for RSS if used
> > + * @pf: board private structure
> > + **/
> > +static s32 i40e_config_rss(struct i40e_pf *pf)
> > +{
> > +	struct i40e_hw *hw = &pf->hw;
> > +	u32 lut = 0;
> > +	int i, j;
> > +	u64 hena;
> > +	/* Set of random keys generated using kernel random number
> generator */
> > +	static const u32 seed[I40E_PFQF_HKEY_MAX_INDEX + 1] = {0x41b01687,
> > +				0x183cfd8c, 0xce880440, 0x580cbc3c, 0x35897377,
> > +				0x328b25e1, 0x4fa98922, 0xb7d90c14, 0xd5bad70d,
> > +				0xcd15a2c1, 0xe8580225, 0x4a1e9d11, 0xfe5731be};
> 
> Chosen by a fair dice roll?

Well, as fair as /dev/random gets.

> 
> [...]
> > +/**
> > + * i40e_assign_netdev_ops - Initialize netdev operations function
> pointers
> > + * @dev: ptr to the netdev struct
> > + **/
> > +static void i40e_assign_netdev_ops(struct net_device *dev)
> > +{
> > +	dev->netdev_ops = &i40e_netdev_ops;
> > +	dev->watchdog_timeo = 5 * HZ;
> > +}
> 
> Sure you need a function for that?

No, probably not anymore.  I think earlier code used this in multiple places, but has since been refactored out.  We'll simplify this further.

> 
> [...]
> > +static s32 i40e_config_netdev(struct i40e_vsi *vsi)
> > +{
> [...]
> > +	if (pf->pci_using_dac)
> > +		netdev->features |= NETIF_F_HIGHDMA;
> [...]
> 
> HIGHDMA just means you don't assume TX page fragments are in lowmem.  It
> actually has nothing to do with DMA capabilities, which are checked
> separately.  Besides which DAC isn't exactly relevant to PCI Express
> devices... so this looks like cargo-culting from e1000 from the days
> before e1000e was split off.

Okay.

> 
> I didn't read any further yet.
> 
> Ben.
> 
> --
> Ben Hutchings, Staff Engineer, Solarflare
> Not speaking for my employer; that's the marketing department's job.
> They asked us to note that Solarflare product names are trademarked.

Thanks for your time and comments,
sln

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