linux-kernel - Re: [PATCH v2] locking: SIX locks (shared/intent/exclusive)

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Message-ID: <ZGw+2abYSDohPG2E@moria.home.lan>
Date:   Tue, 23 May 2023 00:19:37 -0400
From:   Kent Overstreet <kent.overstreet@...ux.dev>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Brian Foster <bfoster@...hat.com>,
        Dave Chinner <dchinner@...hat.com>
Subject: Re: [PATCH v2] locking: SIX locks (shared/intent/exclusive)

On Mon, May 22, 2023 at 03:05:25PM -0700, Boqun Feng wrote:
> > + * bits 29-30		has read waiters
> > + * bits 30-31		has intent waiters
> > + * bits 31-32		has write waiters
> > + */
> > +
> > +#define SIX_LOCK_HELD_read_OFFSET	0
> > +#define SIX_LOCK_HELD_read		~(~0U << 26)
> > +#define SIX_LOCK_HELD_intent		(1U << 26)
> > +#define SIX_LOCK_HELD_write		(1U << 27)
> > +#define SIX_LOCK_WAITING_read		(1U << (28 + SIX_LOCK_read))
> > +#define SIX_LOCK_WAITING_intent		(1U << (28 + SIX_LOCK_intent))
> > +#define SIX_LOCK_WAITING_write		(1U << (28 + SIX_LOCK_write))
> > +#define SIX_LOCK_NOSPIN			(1U << 31)
> 
> ^ NOSPIN is the 31st bit.

Thanks - I think I'll just delete that comment, it's out of date and
the state bits have simplified a bit :)