linux-kernel - Re: [PATCH 1/5] sched: make struct task

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Message-ID: <YCEU3SSoYneIh5t1@hirez.programming.kicks-ass.net>
Date:   Mon, 8 Feb 2021 11:39:25 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     mingo@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] sched: make struct task_struct::state 32-bit

On Sat, Feb 06, 2021 at 06:18:32PM +0300, Alexey Dobriyan wrote:
> 32-bit accesses are shorter than 64-bit accesses on x86_64.
> Nothing uses 64-bitness of struct task_struct::state.
> 
> Propagate 32-bitness to other variables and functions.

You're saving a handful of bytes, why?

> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -655,7 +655,7 @@ struct task_struct {
>  	struct thread_info		thread_info;
>  #endif
>  	/* -1 unrunnable, 0 runnable, >0 stopped: */
> -	volatile long			state;
> +	volatile int			state;

A much larger, but probably more useful cleanup would be to get rid of
that volatile.