Re: [dpdk-dev] [PATCH 1/2] net/netvsc: allow setting rx and tx copy break

[Long Li <longli@microsoft.com>]

> Subject: Re: [dpdk-dev] [PATCH 1/2] net/netvsc: allow setting rx and tx copy
> break
> 
> On 10/22/2020 8:46 PM, Long Li wrote:
> > From: Stephen Hemminger <stephen@networkplumber.org>
> >
> > The values for Rx and Tx copy break should be tunable rather than hard
> > coded constants.
> >
> > The rx_copybreak sets the threshold where the driver uses an external
> > mbuf to avoid having to copy data. Setting 0 for copybreak will cause
> > driver to always create an external mbuf. Setting a value greater than
> > the MTU would prevent it from ever making an external mbuf and always
> > copy. The default value is 256 (bytes).
> >
> > Likewise the tx_copybreak sets the threshold where the driver
> > aggregates multiple small packets into one request. If tx_copybreak is
> > 0 then each packet goes as a VMBus request (no copying).
> > If tx_copybreak is set larger than the MTU, then all packets smaller
> > than the chunk size of the VMBus send buffer will be copied; larger
> > packets always have to go as a single direct request. The default
> > value is 512 (bytes).
> >
> > Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> > Signed-off-by: Long Li <longli@microsoft.com>
> 
> <...>
> 
> > @@ -45,6 +45,10 @@
> >   			    DEV_RX_OFFLOAD_VLAN_STRIP | \
> >   			    DEV_RX_OFFLOAD_RSS_HASH)
> >
> > +#define NETVSC_ARG_LATENCY "latency"
> > +#define NETVSC_ARG_RXBREAK "rx_copybreak"
> > +#define NETVSC_ARG_TXBREAK "tx_copybreak"
> > +
> 
> Can you please document new devargs in the driver documentation?
> 
> <...>
> 
> > @@ -181,12 +167,32 @@ static int hn_parse_args(const struct rte_eth_dev
> *dev)
> >   		return -EINVAL;
> >   	}
> >
> > -	ret = rte_kvargs_process(kvlist, "latency", hn_set_latency, hv);
> > -	if (ret)
> > -		PMD_DRV_LOG(ERR, "Unable to process latency arg\n");
> > +	for (i = 0; i != kvlist->count; ++i) {
> > +		const struct rte_kvargs_pair *pair = &kvlist->pairs[i];
> > +
> > +		if (!strcmp(pair->key, NETVSC_ARG_LATENCY))
> > +			latency = atoi(pair->value);
> > +		else if (!strcmp(pair->key, NETVSC_ARG_RXBREAK))
> > +			rx_break = atoi(pair->value);
> > +		else if (!strcmp(pair->key, NETVSC_ARG_TXBREAK))
> > +			tx_break = atoi(pair->value);
> > +	}
> > +
> 
> Instead of accessing to the kvlist internals, I think better to use
> 'rte_kvargs_process()' as done previously.
> If the reason to remove callback is to not create a callback for each argument, a
> generic one can be used for all.
> 
> > +	if (latency >= 0) {
> > +		PMD_DRV_LOG(DEBUG, "set latency %d usec", latency);
> > +		hv->latency = latency * 1000;	/* usec to nsec */
> > +	}
> > +	if (rx_break >= 0) {
> > +		PMD_DRV_LOG(DEBUG, "rx copy break set to %d", rx_break);
> > +		hv->rx_copybreak = rx_break;
> > +	}
> > +	if (tx_break >= 0) {
> > +		PMD_DRV_LOG(DEBUG, "tx copy break set to %d", tx_break);
> > +		hv->tx_copybreak = tx_break;
> > +	}
> >
> 
> When 'rte_kvargs_process()' used, the valued can be assigned directly to 'hv-
> >tx_copybreak', if the argument is not available, it won't be updated, so above
> check can be dropped.

Thanks Ferruh, I will send V2 to address comments.

Long