linux-kernel - Re: [PATCH V3] sched/rt, powerpc: Prepare for PREEMPT

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Message-ID: <871rgt4gg4.fsf@mpe.ellerman.id.au>
Date:   Mon, 16 Nov 2020 23:46:51 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Wang Qing <wangqing@...o.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Nicholas Piggin <npiggin@...il.com>,
        Jordan Niethe <jniethe5@...il.com>,
        Alistair Popple <alistair@...ple.id.au>,
        Wang Qing <wangqing@...o.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3] sched/rt, powerpc: Prepare for PREEMPT_RT

Wang Qing <wangqing@...o.com> writes:
> PREEMPT_RT is a separate preemption model, CONFIG_PREEMPT will
>  be disabled when CONFIG_PREEMPT_RT is enabled,  so we need
> to add CONFIG_PREEMPT_RT output to __die().
>
> Signed-off-by: Wang Qing <wangqing@...o.com>

Something fairly similar was posted previously.

That time I said:

  I don't think there's any point adding the "_RT" to the __die() output
  until/if we ever start supporting PREEMPT_RT.

  https://lore.kernel.org/linuxppc-dev/87d0ext4q3.fsf@mpe.ellerman.id.au/
   

And I think I still feel the same way. It's not clear powerpc will ever
support PREEMPT_RT, so this would just be confusing to people. And
potentially someone will then send a patch to remove it as dead code.

cheers



> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> index 5006dcb..dec7b81
> --- a/arch/powerpc/kernel/traps.c
> +++ b/arch/powerpc/kernel/traps.c
> @@ -262,10 +262,11 @@ static int __die(const char *str, struct pt_regs *regs, long err)
>  {
>  	printk("Oops: %s, sig: %ld [#%d]\n", str, err, ++die_counter);
>  
> -	printk("%s PAGE_SIZE=%luK%s%s%s%s%s%s %s\n",
> +	printk("%s PAGE_SIZE=%luK%s%s%s%s%s%s%s %s\n",
>  	       IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN) ? "LE" : "BE",
>  	       PAGE_SIZE / 1024, get_mmu_str(),
>  	       IS_ENABLED(CONFIG_PREEMPT) ? " PREEMPT" : "",
> +	       IS_ENABLED(CONFIG_PREEMPT_RT) ? " PREEMPT_RT" : "",
>  	       IS_ENABLED(CONFIG_SMP) ? " SMP" : "",
>  	       IS_ENABLED(CONFIG_SMP) ? (" NR_CPUS=" __stringify(NR_CPUS)) : "",
>  	       debug_pagealloc_enabled() ? " DEBUG_PAGEALLOC" : "",
> -- 
> 2.7.4