linux-kernel - Re: [PATCH] locking/lockdep: Report comm/pid/timestamp information

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Message-ID: <20180709083118.GA2476@hirez.programming.kicks-ass.net>
Date:   Mon, 9 Jul 2018 10:31:18 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Eugeniu Rosca <roscaeugeniu@...il.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Will Deacon <will.deacon@....com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Byungchul Park <byungchul.park@....com>,
        Eugeniu Rosca <erosca@...adit-jv.com>,
        Eugeniu Rosca <rosca.eugeniu@...il.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Subject: Re: [PATCH] locking/lockdep: Report comm/pid/timestamp information

On Mon, Jul 09, 2018 at 02:57:25AM +0200, Eugeniu Rosca wrote:
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index 6fc77d4dbdcd..eeed7ea2e198 100644
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -186,6 +186,10 @@ struct lock_list {
>  	struct list_head		entry;
>  	struct lock_class		*class;
>  	struct stack_trace		trace;
> +	unsigned long long		ts;
> +	char				comm[16];
> +	pid_t				pid;
> +	int				cpu;
>  	int				distance;
>  
>  	/*

Yeah, not going to happen. You grow that structure from 64 bytes to 96
bytes and with that grow the static footprint of the kernel by 512k (in
the very best case) possibly again breaking things like sparc (which
have a strict limit on the kernel image size).

And all that for data that I've never needed and never even considered
useful when looking at lockdep output.