linux-kernel - Re: [PATCH bpf-next v2 11/26] rqspinlock: Add deadlock detection and recovery

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Message-ID: <CAP01T75Z0GjUPiKWCPU7isSMvA+1uMtYE2Nm-iQnvpjFxk0OUQ@mail.gmail.com>
Date: Thu, 13 Feb 2025 07:11:27 +0100
From: Kumar Kartikeya Dwivedi <memxor@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Linus Torvalds <torvalds@...ux-foundation.org>, Will Deacon <will@...nel.org>, 
	Waiman Long <llong@...hat.com>, Alexei Starovoitov <ast@...nel.org>, Andrii Nakryiko <andrii@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Martin KaFai Lau <martin.lau@...nel.org>, 
	Eduard Zingerman <eddyz87@...il.com>, "Paul E. McKenney" <paulmck@...nel.org>, Tejun Heo <tj@...nel.org>, 
	Barret Rhoden <brho@...gle.com>, Josh Don <joshdon@...gle.com>, Dohyun Kim <dohyunkim@...gle.com>, 
	linux-arm-kernel@...ts.infradead.org, kernel-team@...a.com
Subject: Re: [PATCH bpf-next v2 11/26] rqspinlock: Add deadlock detection and recovery

On Mon, 10 Feb 2025 at 11:21, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Thu, Feb 06, 2025 at 02:54:19AM -0800, Kumar Kartikeya Dwivedi wrote:
> > +#define RES_NR_HELD 32
> > +
> > +struct rqspinlock_held {
> > +     int cnt;
> > +     void *locks[RES_NR_HELD];
> > +};
>
> That cnt field makes the whole thing overflow a cacheline boundary.
> Making it 31 makes it fit again.

Makes sense, I can make RES_NR_HELD 31, it doesn't matter too much.
That's one less cacheline to pull into the local CPU during remote CPU reads.