linux-kernel - Re: [PATCH v2 8/9] x86/mm/tlb: Remove UV special case

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Date:   Tue, 9 Jul 2019 21:50:27 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Nadav Amit <namit@...are.com>
cc:     Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Dimitri Sivanich <sivanich@....com>,
        Mike Travis <mike.travis@....com>, Russ Anderson <rja@....com>,
        Hedi Berriche <hedi.berriche@....com>
Subject: Re: [PATCH v2 8/9] x86/mm/tlb: Remove UV special case

On Tue, 2 Jul 2019, Nadav Amit wrote:

> SGI UV support is outdated and not maintained, and it is not clear how
> it performs relatively to non-UV. Remove the code to simplify the code.

You should at least Cc the SGI/HP folks on that. They are still
around. Done so.

> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Suggested-by: Andy Lutomirski <luto@...nel.org>
> Signed-off-by: Nadav Amit <namit@...are.com>
> ---
>  arch/x86/mm/tlb.c | 25 -------------------------
>  1 file changed, 25 deletions(-)
> 
> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
> index b47a71820f35..64afe1215495 100644
> --- a/arch/x86/mm/tlb.c
> +++ b/arch/x86/mm/tlb.c
> @@ -689,31 +689,6 @@ void native_flush_tlb_multi(const struct cpumask *cpumask,
>  		trace_tlb_flush(TLB_REMOTE_SEND_IPI,
>  				(info->end - info->start) >> PAGE_SHIFT);
>  
> -	if (is_uv_system()) {
> -		/*
> -		 * This whole special case is confused.  UV has a "Broadcast
> -		 * Assist Unit", which seems to be a fancy way to send IPIs.
> -		 * Back when x86 used an explicit TLB flush IPI, UV was
> -		 * optimized to use its own mechanism.  These days, x86 uses
> -		 * smp_call_function_many(), but UV still uses a manual IPI,
> -		 * and that IPI's action is out of date -- it does a manual
> -		 * flush instead of calling flush_tlb_func_remote().  This
> -		 * means that the percpu tlb_gen variables won't be updated
> -		 * and we'll do pointless flushes on future context switches.
> -		 *
> -		 * Rather than hooking native_flush_tlb_multi() here, I think
> -		 * that UV should be updated so that smp_call_function_many(),
> -		 * etc, are optimal on UV.
> -		 */
> -		flush_tlb_func_local(info);
> -
> -		cpumask = uv_flush_tlb_others(cpumask, info);
> -		if (cpumask)
> -			smp_call_function_many(cpumask, flush_tlb_func_remote,
> -					       (void *)info, 1);
> -		return;
> -	}
> -
>  	/*
>  	 * If no page tables were freed, we can skip sending IPIs to
>  	 * CPUs in lazy TLB mode. They will flush the CPU themselves
> -- 
> 2.17.1
> 
>