Re: [dpdk-dev] [RFC 01/14] ethdev: add link status read/write functions

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 05 Jan 2018 15:24:48 +0100
Thomas Monjalon <thomas@monjalon.net> wrote:

> Stephen,
> Qiming was suggesting a name change for the functions.
> What do you think?
> 
> 13/10/2017 17:12, Stephen Hemminger:
> > On Wed, 11 Oct 2017 08:32:12 +0000
> > "Yang, Qiming" <qiming.yang@intel.com> wrote:
> >   
> > > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Stephen Hemminger
> > > > Sent: Saturday, July 15, 2017 2:30 AM
> > > > To: dev@dpdk.org
> > > > Cc: Stephen Hemminger <stephen@networkplumber.org>; Stephen Hemminger
> > > > <sthemmin@microsoft.com>
> > > > Subject: [dpdk-dev] [RFC 01/14] ethdev: add link status read/write functions
> > > > 
> > > > Many drivers are all doing copy/paste of the same code to atomicly update the
> > > > link status. Reduce duplication, and allow for future changes by having common
> > > > function for this.
> > > > 
> > > > Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
> > > > ---
> > > >  lib/librte_ether/rte_ethdev.c | 36 ++++++++++++++++++++++++++++++++++++
> > > >  lib/librte_ether/rte_ethdev.h | 28 ++++++++++++++++++++++++++++
> > > >  2 files changed, 64 insertions(+)
> > > > 
> > > > diff --git a/lib/librte_ether/rte_ethdev.c b/lib/librte_ether/rte_ethdev.c index
> > > > a1b744704f3a..7532fc6b65f0 100644
> > > > --- a/lib/librte_ether/rte_ethdev.c
> > > > +++ b/lib/librte_ether/rte_ethdev.c
> > > > @@ -1332,6 +1332,42 @@ rte_eth_link_get_nowait(uint8_t port_id, struct
> > > > rte_eth_link *eth_link)  }
> > > > 
> > > >  int
> > > > +_rte_eth_link_update(struct rte_eth_dev *dev,
> > > > +		    const struct rte_eth_link *link)
> > > > +{
> > > > +	volatile struct rte_eth_link *dev_link = &(dev->data->dev_link);
> > > > +	struct rte_eth_link old;
> > > > +
> > > > +	RTE_BUILD_BUG_ON(sizeof(*link) != sizeof(uint64_t));
> > > > +
> > > > +	old = *dev_link;
> > > > +
> > > > +	/* Only reason we use cmpset rather than set is
> > > > +	 * that on some architecture may use sign bit as a flag value.
> > > > +	 */
> > > > +	while (rte_atomic64_cmpset((volatile uint64_t *)dev_link,
> > > > +				    *(volatile uint64_t *)dev_link,
> > > > +				   *(const uint64_t *)link) == 0)
> > > > +		continue;
> > > > +
> > > > +	return (old.link_status == link->link_status) ? -1 : 0; }
> > > > +
> > > > +void _rte_eth_link_read(struct rte_eth_dev *dev,
> > > > +			struct rte_eth_link *link)
> > > > +{
> > > > +	const uint64_t *src = (const uint64_t *)&(dev->data->dev_link);
> > > > +	volatile uint64_t *dst = (uint64_t *)link;
> > > > +
> > > > +	RTE_BUILD_BUG_ON(sizeof(*link) != sizeof(uint64_t));
> > > > +
> > > > +	/* Note: this should never fail since both destination and expected
> > > > +	 * values are the same and are a pointer from caller.
> > > > +	 */
> > > > +	rte_atomic64_cmpset(dst, *dst, *src);
> > > > +}
> > > > +
> > > > +int
> > > >  rte_eth_stats_get(uint8_t port_id, struct rte_eth_stats *stats)  {
> > > >  	struct rte_eth_dev *dev;
> > > > diff --git a/lib/librte_ether/rte_ethdev.h b/lib/librte_ether/rte_ethdev.h index
> > > > f6837278521c..974657933f23 100644
> > > > --- a/lib/librte_ether/rte_ethdev.h
> > > > +++ b/lib/librte_ether/rte_ethdev.h
> > > > @@ -2219,6 +2219,34 @@ void rte_eth_link_get(uint8_t port_id, struct
> > > > rte_eth_link *link);
> > > >   */
> > > >  void rte_eth_link_get_nowait(uint8_t port_id, struct rte_eth_link *link);
> > > > 
> > > > +
> > > > +/**
> > > > + * @internal
> > > > + * Atomically write the link status for the specific device.
> > > > + * It is for use by DPDK device driver use only.
> > > > + * User applications should not call it
> > > > + *
> > > > + * @param dev
> > > > + *  Pointer to struct rte_eth_dev.
> > > > + * @param link
> > > > + *  New link status value.
> > > > + * @return
> > > > + *  -1 if link state has changed, 0 if the same.
> > > > + */
> > > > +int _rte_eth_link_update(struct rte_eth_dev *dev,
> > > > +			 const struct rte_eth_link *link);
> > > > +    
> > > This function is only do the atomically write, what do you think to change the function name to _rte_eth_atomic_write_link_status,
> > > Use name link_update makes me confused, and mix up it with dev_ops link_update.  
> > > > +/**
> > > > + * @internal
> > > > + * Atomically read the link speed and status.
> > > > + * @param dev
> > > > + *  Pointer to struct rte_eth_dev.
> > > > + * @param link
> > > > + *  link status value.
> > > > + */
> > > > +void _rte_eth_link_read(struct rte_eth_dev *dev,
> > > > +			struct rte_eth_link *link);
> > > > +    
> > > This name is also not very clear. I think change to _rte_eth_atomic_read_link_status will better.  
> > > >  /**
> > > >   * Retrieve the general I/O statistics of an Ethernet device.
> > > >   *
> > > > --
> > > > 2.11.0    
> > >   
> > 
> > The first set of  patches was just  trying to combine multiple copies of same code.
> > Every place  was doing same thing for atomic update.  

I would just change the name to linkstatsus update.
Also since writes of unsigned long are guaranteed atomic, the code could
be optimized on 64bit platforms.