linux-kernel - Re: [PATCH] entry: always inline local_irq_{enable,disable}_exit_to

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Message-ID: <20251205124513.GZ2528459@noisy.programming.kicks-ass.net>
Date: Fri, 5 Dec 2025 13:45:13 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Andy Lutomirski <luto@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH] entry: always inline
 local_irq_{enable,disable}_exit_to_user()

On Fri, Dec 05, 2025 at 02:54:26AM -0800, Eric Dumazet wrote:
> On Fri, Dec 5, 2025 at 2:51 AM Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > On Thu, Dec 04, 2025 at 03:31:27PM +0000, Eric Dumazet wrote:
> > > clang needs __always_inline instead of inline, even for tiny helpers.
> > >
> > > This saves some cycles in system call fast path, and saves 195 bytes
> > > on x86_64 build:
> > >
> > > $ size vmlinux.before vmlinux.after
> > >    text          data     bss     dec     hex filename
> > > 34652814      22291961        5875180 62819955        3be8e73 vmlinux.before
> > > 34652619      22291961        5875180 62819760        3be8db0 vmlinux.after
> > >
> > > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> >
> > Yeah, sometimes these inline heuristics drive me mad. I've picked up
> > this and the rseq one. I'll do something with them after rc1.
> 
> Thanks Peter.
> 
> I forgot to include perf numbers for this one, but apparently having a
>  local_irq_enable()
> in an out-of-line function in syscall path was adding a 5 % penalty on
> some platforms.
> 
> Crazy...

Earlier Zen with RET mitigation? ;-)