linux-kernel - Re: [PATCH v3 8/9] x86/mm/tlb: Remove UV special case

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Message-ID: <54c082c5-ebee-8fd7-cf69-b8c15b60a329@hpe.com>
Date:   Thu, 18 Jul 2019 19:25:29 -0700
From:   Mike Travis <mike.travis@....com>
To:     Nadav Amit <namit@...are.com>, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCH v3 8/9] x86/mm/tlb: Remove UV special case

It is a fact that the UV is still the UV and SGI is now part of HPE. 
The current external product is known as SuperDome Flex.  It is both up 
to date as well as very well maintained.  The ACK I provided was an okay 
to change the code, but please make the description accurate.

On 7/18/2019 5:58 PM, 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 SGI UV support is outdated and not maintained, and it is not clear how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.
> 
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Acked-by: Mike Travis <mike.travis@....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 89f83ad19507..40daad52ec7d 100644
> --- a/arch/x86/mm/tlb.c
> +++ b/arch/x86/mm/tlb.c
> @@ -684,31 +684,6 @@ 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 -		 * and that IPI's action is out of date -- it does a manual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((void *)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
>