linux-kernel - Re: [RFC 1/1] eventpoll: support busy poll per epoll instance

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Date: Mon, 22 Jan 2024 16:25:01 +0100
From: Christian Brauner <brauner@...nel.org>
To: Joe Damato <jdamato@...tly.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	chuck.lever@...cle.com, jlayton@...nel.org, linux-api@...r.kernel.org, 
	edumazet@...gle.com, davem@...emloft.net, alexander.duyck@...il.com, 
	sridhar.samudrala@...el.com, kuba@...nel.org
Subject: Re: [RFC 1/1] eventpoll: support busy poll per epoll instance

On Sat, Jan 20, 2024 at 12:42:47AM +0000, Joe Damato wrote:
> Add F_EPOLL_{S,G}ET_BUSY_POLL_USECS to allow setting a busy poll timeout
> per epoll instance so that individual applications can enable (or
> disable) epoll based busy poll as needed.
> 
> Prior to this change, epoll-based busy poll could only be enabled
> system-wide, which limits the usefulness of busy poll.
> 
> Signed-off-by: Joe Damato <jdamato@...tly.com>
> ---

This should be an ioctl on the epoll fd, not a fcntl(). fcntl()s
should aim to be generic which this isn't. We've recently rejected a
memfd addition as a fcntl() as well for the same reason.