linux-kernel - Re: [PATCH 12/14] sparc64: rtrap: Remove unneeded need

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Message-Id: <20190311.161313.458909688496508375.davem@davemloft.net>
Date:   Mon, 11 Mar 2019 16:13:13 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     valentin.schneider@....com
Cc:     linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org
Subject: Re: [PATCH 12/14] sparc64: rtrap: Remove unneeded need_resched()
 loop

From: Valentin Schneider <valentin.schneider@....com>
Date: Mon, 11 Mar 2019 22:47:50 +0000

> Since the enabling and disabling of IRQs within preempt_schedule_irq()
> is contained in a need_resched() loop, we don't need the outer arch
> code loop.
> 
> We seem to be looping back somewhere much higher than the usual
> preempt/need_resched checks, but AFAICT we would just branch to
> 'rtrap_no_irq_enable' and then back to 'to_kernel', which is
> a need_resched() loop with a few extra steps.
> 
> Signed-off-by: Valentin Schneider <valentin.schneider@....com>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: sparclinux@...r.kernel.org
> ---
>  arch/sparc/kernel/rtrap_64.S | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/arch/sparc/kernel/rtrap_64.S b/arch/sparc/kernel/rtrap_64.S
> index 29aa34f11720..57fb75686957 100644
> --- a/arch/sparc/kernel/rtrap_64.S
> +++ b/arch/sparc/kernel/rtrap_64.S
> @@ -322,7 +322,6 @@ to_kernel:
>  		 nop
>  		call			preempt_schedule_irq
>  		 nop
> -		ba,pt			%xcc, rtrap
>  #endif
>  kern_fpucheck:	ldub			[%g6 + TI_FPDEPTH], %l5
>  		brz,pt			%l5, rt_continue
> -- 
> 2.20.1
> 

We must re-evaluate the %tstate value stored in ptregs, you cannot
make this change.