linux-kernel - Re: [PATCH 04/11] PM: EM: Add the infrastructure for command processing.

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Message-ID: <be23f55c-329c-444d-b5d8-83ae29b05387@igalia.com>
Date: Wed, 4 Jun 2025 18:11:02 +0200
From: Changwoo Min <changwoo@...lia.com>
To: Lukas Wunner <lukas@...ner.de>
Cc: lukasz.luba@....com, rafael@...nel.org, len.brown@...el.com,
 pavel@...nel.org, christian.loehle@....com, tj@...nel.org,
 kernel-dev@...lia.com, linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/11] PM: EM: Add the infrastructure for command
 processing.

On 6/2/25 04:59, Lukas Wunner wrote:
> On Thu, May 29, 2025 at 09:13:08AM +0900, Changwoo Min wrote:
>> +static int em_genl_cmd_doit(struct sk_buff *skb, struct genl_info *info)
>> +{
>> +	struct param p = { .attrs = info->attrs };
>> +	struct sk_buff *msg;
>> +	void *hdr;
>> +	int cmd = info->genlhdr->cmd;
>> +	int ret = -EMSGSIZE;
>> +
>> +	msg = genlmsg_new(NLMSG_GOODSIZE, GFP_KERNEL);
>> +	if (!msg)
>> +		return -ENOMEM;
> 
> Just a heads-up, I know everyone recommends NLMSG_GOODSIZE but in reality
> it's not that great because netlink_trim() reallocates the skb and copies
> the entire linear buffer if it determines that the skb is half-empty.
> Performance suffers as a result.  So it's actually better to calculate
> the exact message length prior to allocation.
Thank you, Lukas, for sharing the experience. I will address it in the
next version.

Regards,
Changwoo Min