linux-kernel - Re: [PATCH 0/4] Fix ebizzy performance regression due to X86 TLB range flush v2

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Date:	Fri, 20 Dec 2013 13:20:19 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alex Shi <alex.shi@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	H Peter Anvin <hpa@...or.com>, Linux-X86 <x86@...nel.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 0/4] Fix ebizzy performance regression due to X86 TLB
 range flush v2


* Mel Gorman <mgorman@...e.de> wrote:

> tlb_flushall_shift == -1	Always use flush all
> tlb_flushall_shift == 1		Aggressively use individual flushes
> tlb_flushall_shift == 6		Conservatively use individual flushes
> 
> IvyBridge was too aggressive using individual flushes and my patch 
> makes it less aggressive.
> 
> Intel's code for this currently looks like
> 
>         switch ((c->x86 << 8) + c->x86_model) {
>         case 0x60f: /* original 65 nm celeron/pentium/core2/xeon, "Merom"/"Conroe" */
>         case 0x616: /* single-core 65 nm celeron/core2solo "Merom-L"/"Conroe-L" */
>         case 0x617: /* current 45 nm celeron/core2/xeon "Penryn"/"Wolfdale" */
>         case 0x61d: /* six-core 45 nm xeon "Dunnington" */
>                 tlb_flushall_shift = -1;
>                 break;
>         case 0x61a: /* 45 nm nehalem, "Bloomfield" */
>         case 0x61e: /* 45 nm nehalem, "Lynnfield" */
>         case 0x625: /* 32 nm nehalem, "Clarkdale" */
>         case 0x62c: /* 32 nm nehalem, "Gulftown" */
>         case 0x62e: /* 45 nm nehalem-ex, "Beckton" */
>         case 0x62f: /* 32 nm Xeon E7 */
>                 tlb_flushall_shift = 6;
>                 break;
>         case 0x62a: /* SandyBridge */
>         case 0x62d: /* SandyBridge, "Romely-EP" */
>                 tlb_flushall_shift = 5;
>                 break;
>         case 0x63a: /* Ivybridge */
>                 tlb_flushall_shift = 2;
>                 break;
>         default:
>                 tlb_flushall_shift = 6;
>         }
> 
> That default shift of "6" is already conservative which is why I 
> don't think we need to change anything there. AMD is slightly more 
> aggressive in their choices but not enough to panic.

Lets face it, the per model tunings are most likely crap: the only 
place where it significantly deviated from '6' was Ivybridge - and 
there it was causing a regression.

With your patch we'll have 6 everywhere, except on SandyBridge where 
it's slightly more agressive at 5 - which is probably noise.

So my argument is that we should use '6' _everywhere_ and do away with 
the pretense that we do per model tunings...

Thanks,

	Ingo
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