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 05:31:59PM +0000, Traynor, Kevin wrote:
> 
> > -----Original Message-----
> > From: Ananyev, Konstantin
> > Sent: Tuesday, October 27, 2015 12:13 PM
> > To: Richardson, Bruce; Traynor, Kevin
> > Cc: dev@dpdk.org
> > Subject: RE: [dpdk-dev] [PATCH] ixgbe: change logging for ixgbe tx code path
> > selection
> > 
> > 
> > 
> > > -----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
> 
> yeah, sure. I agree with changing for 1. I also agree with Konstantin re commas.
> The code under the dangling else is aligned incorrectly/correctly depending on
> whether the #ifdef is true or not, so I think adding multiple statements with {}
> now will make it obvious for the next person who modifies.
> 
Final alternative is to have a switch statement at the end of the block for
printing based on what the final function selection is. That way there is only
a single assignment needed and no awkward braces. :-)