netdev - Re: [PATCH net-next v10 2/4] ethtool: provide customized dim profile management

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Date: Mon, 29 Apr 2024 10:47:41 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Heng Qi <hengqi@...ux.alibaba.com>
Cc: netdev@...r.kernel.org, virtualization@...ts.linux.dev, "David S .
 Miller" <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>, Eric
 Dumazet <edumazet@...gle.com>, Jason Wang <jasowang@...hat.com>, "Michael S
 . Tsirkin" <mst@...hat.com>, Brett Creeley <bcreeley@....com>, Ratheesh
 Kannoth <rkannoth@...vell.com>, Alexander Lobakin
 <aleksander.lobakin@...el.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Tal
 Gilboa <talgi@...dia.com>, Jonathan Corbet <corbet@....net>,
 linux-doc@...r.kernel.org, Maxime Chevallier
 <maxime.chevallier@...tlin.com>, Jiri Pirko <jiri@...nulli.us>, Paul
 Greenwalt <paul.greenwalt@...el.com>, Ahmed Zaki <ahmed.zaki@...el.com>,
 Vladimir Oltean <vladimir.oltean@....com>, Kory Maincent
 <kory.maincent@...tlin.com>, Andrew Lunn <andrew@...n.ch>, "justinstitt @
 google . com" <justinstitt@...gle.com>
Subject: Re: [PATCH net-next v10 2/4] ethtool: provide customized dim
 profile management

On Sun, 28 Apr 2024 22:49:09 +0800 Heng Qi wrote:
> >> +#if IS_ENABLED(CONFIG_DIMLIB)
> >> +	if (dev->irq_moder) {  
> > This may be NULL  
> 
> 
> Do you mean dev may be null or dev->irq_moder may be null?
> The former has been excluded (see const struct ethtool_ops *ops
> 
> = req_info->dev->ethtool_ops;).
> 
> And we are ruling out the latter using 'if (dev->irq_moder)'.
> 
> Or something else?

Hm, I must have misread something here.

> >> +	nla_for_each_nested_type(nest, ETHTOOL_A_PROFILE_IRQ_MODERATION, nests, rem) {
> >> +		ret = nla_parse_nested(moder,
> >> +				       ARRAY_SIZE(coalesce_irq_moderation_policy) - 1,
> >> +				       nest, coalesce_irq_moderation_policy,
> >> +				       extack);
> >> +		if (ret)
> >> +			return ret;
> >> +
> >> +		if (!NL_REQ_ATTR_CHECK(extack, nest, moder, ETHTOOL_A_IRQ_MODERATION_USEC)) {
> >> +			if (irq_moder->coal_flags & DIM_COALESCE_USEC)  
> > There are 3 options here, not 2:
> >
> > 	if (irq_moder->coal_flags & flag) {
> > 		if (NL_REQ_ATTR_CHECK())
> > 			val = nla_get_u32(...);
> > 		else
> > 			return -EINVAL;
> > 	} else {
> > 		if (moder[attr_type)) {
> > 			BAD_ATTR()
> > 			return -EOPNOTSUPP;
> > 		}
> > 	}  
> 
> Maybe we missed something.
> 
> As shown in the commit log, the user is allowed to modify only
> a certain fields in irq-moderation. It is assumed that the driver
> supports modification of usec and pkts, but the user may only
> modify usec and only fill in the usec attr.
> 
> Therefore, the kernel only gets usec attr here. Of course, the user
> may have passed in 5 groups of "n, n, n", which means that nothing
> is modified, and rx_profile and irq_moderation attrs are all empty.

What you describe sounds good, but it's not what the code seems to be
doing. NL_REQ_ATTR_CHECK() will set an error attribute if the attr is
not present.