netdev - Re: [PATCH net-next 2/5] netdev-genl: Dump napi_defer_hard

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Message-ID: <20240829150828.2ec79b73@kernel.org>
Date: Thu, 29 Aug 2024 15:08:28 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Joe Damato <jdamato@...tly.com>
Cc: netdev@...r.kernel.org, edumazet@...gle.com, amritha.nambiar@...el.com,
 sridhar.samudrala@...el.com, sdf@...ichev.me, bjorn@...osinc.com,
 hch@...radead.org, willy@...radead.org, willemdebruijn.kernel@...il.com,
 skhawaja@...gle.com, Martin Karsten <mkarsten@...terloo.ca>, Donald Hunter
 <donald.hunter@...il.com>, "David S. Miller" <davem@...emloft.net>, Paolo
 Abeni <pabeni@...hat.com>, Jesper Dangaard Brouer <hawk@...nel.org>, Xuan
 Zhuo <xuanzhuo@...ux.alibaba.com>, Daniel Jurgens <danielj@...dia.com>,
 linux-kernel@...r.kernel.org (open list)
Subject: Re: [PATCH net-next 2/5] netdev-genl: Dump napi_defer_hard_irqs

On Thu, 29 Aug 2024 13:11:58 +0000 Joe Damato wrote:
> diff --git a/Documentation/netlink/specs/netdev.yaml b/Documentation/netlink/specs/netdev.yaml
> index 959755be4d7f..ee4f99fd4574 100644
> --- a/Documentation/netlink/specs/netdev.yaml
> +++ b/Documentation/netlink/specs/netdev.yaml
> @@ -244,6 +244,11 @@ attribute-sets:
>               threaded mode. If NAPI is not in threaded mode (i.e. uses normal
>               softirq context), the attribute will be absent.
>          type: u32
> +      -
> +        name: defer-hard-irqs
> +        doc: The number of consecutive empty polls before IRQ deferral ends
> +             and hardware IRQs are re-enabled.
> +        type: s32

Why is this a signed value? 🤔️
You can use:

	check:
		max: s32-max

to have netlink validate the overflow if you switch to u32.

>    -
>      name: queue
>      attributes:

> @@ -188,6 +189,10 @@ netdev_nl_napi_fill_one(struct sk_buff *rsp, struct napi_struct *napi,
>  			goto nla_put_failure;
>  	}
>  
> +	napi_defer_hard_irqs = napi_get_defer_hard_irqs(napi);

Here, for example the READ_ONCE() wouldn't have been necessary, right?
Cause we are holding rtnl_lock(), just a random thought, not really
actionable.

> +	if (nla_put_s32(rsp, NETDEV_A_NAPI_DEFER_HARD_IRQS, napi_defer_hard_irqs))
> +		goto nla_put_failure;