linux-kernel - Re: [PATCH 06/14] MIPS: entry: Remove unneeded need

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Message-ID: <alpine.LFD.2.21.1905101706440.12665@eddie.linux-mips.org>
Date:   Fri, 10 May 2019 17:16:56 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@...ux-mips.org>
To:     Paul Burton <paul.burton@...s.com>
cc:     Valentin Schneider <valentin.schneider@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>
Subject: Re: [PATCH 06/14] MIPS: entry: Remove unneeded need_resched() loop

On Thu, 14 Mar 2019, Paul Burton wrote:

> > @@ -66,7 +65,7 @@ need_resched:
> >  	andi	t0, 1
> >  	beqz	t0, restore_all
> >  	jal	preempt_schedule_irq
> > -	b	need_resched
> > +	j	restore_all
> 
> One nit - why change from branch to jump? It's not a big deal, but I'd
> prefer we stick with the branch ("b") instruction for a few reasons:
> 
> - restore_all is nearby so there's no issue with it being out of range
>   of a branch in any variation of the MIPS ISA.

 FYI, if it does go out of range for whatever reason, then for non-PIC 
code GAS will relax it to a jump anyway (with a relocation attached); for 
the regular MIPS ISA that is, where it has been doing that since forever 
(I meant to implement this for the microMIPS ISA too, but IIRC there was a 
complication there, probably coming from the existing more complex branch 
relaxation code and/or slightly different use of relocations, and then it 
fell through the cracks).

  Maciej