linux-kernel - Re: [PATCH 3/3] arm64, mm: Use IPIs for TLB invalidation.

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Date:	Mon, 13 Jul 2015 19:17:55 +0100
From:	Will Deacon <will.deacon@....com>
To:	David Daney <ddaney.cavm@...il.com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Robert Richter <rrichter@...ium.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Daney <david.daney@...ium.com>
Subject: Re: [PATCH 3/3] arm64, mm: Use IPIs for TLB invalidation.

On Sat, Jul 11, 2015 at 09:25:23PM +0100, David Daney wrote:
> From: David Daney <david.daney@...ium.com>
> 
> Most broadcast TLB invalidations are unnecessary.  So when
> invalidating for a given mm/vma target the only the needed CPUs via
> and IPI.
> 
> For global TLB invalidations, also use IPI.
> 
> Tested on Cavium ThunderX.
> 
> This change reduces 'time make -j48' on kernel from 139s to 116s (83%
> as long).

Any idea *why* you're seeing such an improvement? Some older kernels had
a bug where we'd try to flush a negative (i.e. huge) range by page, so it
would be nice to rule that out. I assume these measurements are using
mainline?

Having TLBI responsible for that amount of a kernel build doesn't feel
right to me and doesn't line-up with the profiles I'm used to seeing.

You have 16-bit ASIDs, right?

Will
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