Subject: Re: [PATCH net-next v11 2/4] ethtool: provide customized dim profile management

From: Heng Qi <[email-masked]>
Date: Sat, 4 May 2024 14:32:55 +0800

On Fri, 3 May 2024 14:52:44 +0100, Simon Horman <[email-masked]> wrote:
> On Wed, May 01, 2024 at 01:31:34AM +0800, Heng Qi wrote:
> 
> ...
> 
> > diff --git a/include/linux/dim.h b/include/linux/dim.h
> 
> ...
> 
> > @@ -198,6 +234,32 @@ enum dim_step_result {
> >  	DIM_ON_EDGE,
> >  };
> >  
> > +/**
> > + * net_dim_init_irq_moder - collect information to initialize irq moderation
> > + * @dev: target network device
> > + * @profile_flags: Rx or Tx profile modification capability
> > + * @coal_flags: irq moderation params flags
> > + * @rx_mode: CQ period mode for Rx
> > + * @tx_mode: CQ period mode for Tx
> > + * @rx_dim_work: Rx worker called after dim decision
> > + *    void (*rx_dim_work)(struct work_struct *work);
> > + *
> > + * @tx_dim_work: Tx worker called after dim decision
> > + *    void (*tx_dim_work)(struct work_struct *work);
> > + *
> 
> Hi Heng Qi,

Hi Simon,

> 
> The above seems to result in make htmldocs issuing the following warnings:
> 
>  .../net_dim:175: ./include/linux/dim.h:244: WARNING: Inline emphasis start-string without end-string.
>  .../net_dim:175: ./include/linux/dim.h:244: WARNING: Inline emphasis start-string without end-string.
>  .../net_dim:175: ./include/linux/dim.h:247: WARNING: Inline emphasis start-string without end-string.
>  .../net_dim:175: ./include/linux/dim.h:247: WARNING: Inline emphasis start-string without end-string.
> 
> I suggest the following alternative:
> 
>  * @rx_dim_work: Rx worker called after dim decision
>  * @tx_dim_work: Tx worker called after dim decision

Will update this.

> 
> Exercised using Sphinx 7.2.6
> 
> ...
> 
> > diff --git a/net/ethtool/coalesce.c b/net/ethtool/coalesce.c
> 
> ...
> 
> > @@ -134,6 +212,12 @@ static int coalesce_fill_reply(struct sk_buff *skb,
> >  	const struct coalesce_reply_data *data = COALESCE_REPDATA(reply_base);
> >  	const struct kernel_ethtool_coalesce *kcoal = &data->kernel_coalesce;
> >  	const struct ethtool_coalesce *coal = &data->coalesce;
> > +#if IS_ENABLED(CONFIG_DIMLIB)
> > +	struct net_device *dev = req_base->dev;
> > +	struct dim_irq_moder *moder = dev->irq_moder;
> > +	u8 coal_flags;
> > +	int ret;
> > +#endif
> >  	u32 supported = data->supported_params;
> 
> It's a minor nit, but here goes: please consider using reverse xmas tree
> order - longest line to shortest - for local variable declarations in
> Networking code.
> 
> In this case, I appreciate that it's not strictly possible without
> introducing more than one IS_ENABLED condition, which seems worse.
> So, as that condition breaks the visual flow, what I suggest in this
> case is having a second block of local variable declarations, like this:
> 
> 	const struct coalesce_reply_data *data = COALESCE_REPDATA(reply_base);
> 	const struct kernel_ethtool_coalesce *kcoal = &data->kernel_coalesce;
> 	const struct ethtool_coalesce *coal = &data->coalesce;
> 	u32 supported = data->supported_params;                  
> 
> #if IS_ENABLED(CONFIG_DIMLIB)
> 	struct dim_irq_moder *moder = dev->irq_moder;
> 	struct net_device *dev = req_base->dev;

Note: The line above depends on the line below. :)

However, even so, I will try to make a change to keep "xmas tree order".

> 	u8 coal_flags;
> 	int ret;
> #endif 
> 
> Or better still, if it can be done cleanly, moving all the IS_ENABLED()
> code in this function into a separate function, with an no-op
> implementation in the case that CONFIG_DIMLIB is not enabled. In general
> I'd recommend that approach over sprinkling IS_ENABLED or #ifdef inside
> functions. Because in my experience it tends to lead to more readable code.
> 

As discussed in the previous replies, IS_ENABLED(CONFIG_DIMLIB) will be removed
in the next version, so we'll do not have this problem, but your suggestion is
good.

Thanks.

> In any case, the following tool is helpful for isolating
> reverse xmas tree issues.
> 
> https://github.com/ecree-solarflare/xmastree
> 
> 
> >  	if (coalesce_put_u32(skb, ETHTOOL_A_COALESCE_RX_USECS,
> > @@ -192,11 +276,49 @@ static int coalesce_fill_reply(struct sk_buff *skb,
> >  			     kcoal->tx_aggr_time_usecs, supported))
> >  		return -EMSGSIZE;
> >  
> > +#if IS_ENABLED(CONFIG_DIMLIB)
> > +	if (!moder)
> > +		return 0;
> > +
> > +	coal_flags = moder->coal_flags;
> > +	rcu_read_lock();
> > +	if (moder->profile_flags & DIM_PROFILE_RX) {
> > +		ret = coalesce_put_profile(skb, ETHTOOL_A_COALESCE_RX_PROFILE,
> > +					   rcu_dereference(moder->rx_profile),
> > +					   coal_flags);
> > +		if (ret) {
> > +			rcu_read_unlock();
> > +			return ret;
> > +		}
> > +	}
> > +
> > +	if (moder->profile_flags & DIM_PROFILE_TX) {
> > +		ret = coalesce_put_profile(skb, ETHTOOL_A_COALESCE_TX_PROFILE,
> > +					   rcu_dereference(moder->tx_profile),
> > +					   coal_flags);
> > +		if (ret) {
> > +			rcu_read_unlock();
> > +			return ret;
> > +		}
> > +	}
> > +	rcu_read_unlock();
> > +#endif
> >  	return 0;
> >  }
> 
> ...