linux-kernel - Re: [PATCH v2 1/4] seqlock: introduce scoped_seqlock_read() and scoped_seqlock_read

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Message-ID: <CAHk-=wh5oLhtvxqTv9-rANYAaA+juN-kfdnbpqP2VpzzZYTTyA@mail.gmail.com>
Date: Thu, 9 Oct 2025 16:26:23 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Oleg Nesterov <oleg@...hat.com>, Alexander Viro <viro@...iv.linux.org.uk>, 
	Boqun Feng <boqun.feng@...il.com>, David Howells <dhowells@...hat.com>, 
	Ingo Molnar <mingo@...hat.com>, Li RongQing <lirongqing@...du.com>, 
	Waiman Long <longman@...hat.com>, Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/4] seqlock: introduce scoped_seqlock_read() and scoped_seqlock_read_irqsave()

On Thu, 9 Oct 2025 at 16:20, Peter Zijlstra <peterz@...radead.org> wrote:
>
> The moment I use a union gcc-14 creates the whole structure on the
> stack, while without the union it mostly manages to keep the things
> in registers without too much spilling.

Ouch.

Do the union manually like I did by just using a "unsigned long" for
both 'seq' and 'flags'.

I bet that works fine - it seemed to work well for my - admittedly
somewhat different - version.

              Linus