Re: [dpdk-dev] [PATCH] ixgbe: change logging for ixgbe tx code path selection

[Bruce Richardson <bruce.richardson@intel.com>]

On Tue, Oct 27, 2015 at 12:12:39PM +0000, Ananyev, Konstantin wrote:
> 
> 
> > -----Original Message-----
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Bruce Richardson
> > Sent: Tuesday, October 27, 2015 11:50 AM
> > To: Traynor, Kevin
> > Cc: dev@dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH] ixgbe: change logging for ixgbe tx code path selection
> > 
> > On Tue, Oct 27, 2015 at 11:41:08AM +0000, Kevin Traynor wrote:
> > > Simple and vector are different tx code paths. If vector
> > > is selected, change logging from:
> > > PMD: ixgbe_set_tx_function(): Using simple tx code path
> > > PMD: ixgbe_set_tx_function(): Vector tx enabled.
> > >
> > > to:
> > > PMD: ixgbe_set_tx_function(): Using vector tx code path
> > >
> > > or, if simple selected:
> > > PMD: ixgbe_set_tx_function(): Using simple tx code path
> > >
> > > The dangling else in the #ifdef makes readability difficult,
> > > so resolving in way that seems most readable.
> > >
> > > Signed-off-by: Kevin Traynor <kevin.traynor@intel.com>
> > > ---
> > >  drivers/net/ixgbe/ixgbe_rxtx.c |    8 +++++---
> > >  1 files changed, 5 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c b/drivers/net/ixgbe/ixgbe_rxtx.c
> > > index a598a72..11d7feb 100644
> > > --- a/drivers/net/ixgbe/ixgbe_rxtx.c
> > > +++ b/drivers/net/ixgbe/ixgbe_rxtx.c
> > > @@ -1963,16 +1963,18 @@ ixgbe_set_tx_function(struct rte_eth_dev *dev, struct ixgbe_tx_queue *txq)
> > >  	/* Use a simple Tx queue (no offloads, no multi segs) if possible */
> > >  	if (((txq->txq_flags & IXGBE_SIMPLE_FLAGS) == IXGBE_SIMPLE_FLAGS)
> > >  			&& (txq->tx_rs_thresh >= RTE_PMD_IXGBE_TX_MAX_BURST)) {
> > > -		PMD_INIT_LOG(DEBUG, "Using simple tx code path");
> > >  #ifdef RTE_IXGBE_INC_VECTOR
> > >  		if (txq->tx_rs_thresh <= RTE_IXGBE_TX_MAX_FREE_BUF_SZ &&
> > >  				(rte_eal_process_type() != RTE_PROC_PRIMARY ||
> > >  					ixgbe_txq_vec_setup(txq) == 0)) {
> > > -			PMD_INIT_LOG(DEBUG, "Vector tx enabled.");
> > > +			PMD_INIT_LOG(DEBUG, "Using vector tx code path");
> > >  			dev->tx_pkt_burst = ixgbe_xmit_pkts_vec;
> > >  		} else
> > >  #endif
> > > -		dev->tx_pkt_burst = ixgbe_xmit_pkts_simple;
> > > +		{
> > > +			PMD_INIT_LOG(DEBUG, "Using simple tx code path");
> > > +			dev->tx_pkt_burst = ixgbe_xmit_pkts_simple;
> > > +		}
> > >  	} else {
> > >  		PMD_INIT_LOG(DEBUG, "Using full-featured tx code path");
> > >  		PMD_INIT_LOG(DEBUG,
> > > --
> > > 1.7.4.1
> > >
> > Hi Kevin,
> > 
> > can I suggest a slight alternative here that might help make things easier.
> > Instead of printing the message as we pick the code path, why not have a "logmsg"
> > pointer variable that is assigned in the code, and then print out the log path
> > at the end.
> > 
> > This would have a number of advantages:
> > 1. there are no issues with changing our mind, so we can assign one path type,
> > and then later change it to something different without cluttering up the debug
> > output with the history of our code's flow.
> > 2. it means that you don't have a problem with smaller else legs as you can
> > easily do multiple assignments in the one line using a comma as:
> > 	dev->tx_pkt_burst = ixgbe_xmit_pkts_simple, logmsg = "Using simple ...";
> 
> While I like approach with logmsg, please avoid commas here.
> It will make this peace of code even more hard to read (at least for me).
> Konstantin 
> 

Sure, it's a matter of taste. I'd much prefer a single line with commas to the
awkwardness above trying to manage braces around an ifdef. I'll leave it to 
Kevin to see what he comes up with. :-)

/Bruce