linux-kernel - Re: [tip:sched/core] sched/idle: Micro-optimize the idle loop

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Message-ID: <20171026134136.GR3165@worktop.lehotels.local>
Date:   Thu, 26 Oct 2017 15:41:36 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     cj.chengjian@...wei.com, tglx@...utronix.de, hpa@...or.com,
        linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
        mingo@...nel.org
Cc:     linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/core] sched/idle: Micro-optimize the idle loop

On Thu, Oct 26, 2017 at 02:31:34AM -0700, tip-bot for Cheng Jian wrote:
> After patch (execution in loop):
> 	872:       0f ae e8                lfence

> ARM64:

> After patch (execution in loop):
> 	c84:       d5033d9f        dsb     ld

> @@ -225,7 +226,7 @@ static void do_idle(void)
>  		check_pgt_cache();
>  		rmb();

I never could find a reason for that rmb() to exist, it also lacks a
clarifying comment.

We should perhaps attempt removing that...