linux-kernel - PCID and TLB flushes (was: [GIT PULL] kdbus for 4.1-rc1)

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Message-ID: <20150428221553.GA5770@node.dhcp.inet.fi>
Date:	Wed, 29 Apr 2015 01:15:53 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Andy Lutomirski <luto@...capital.net>,
	Dave Hansen <dave.hansen@...el.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org
Subject: PCID and TLB flushes (was: [GIT PULL] kdbus for 4.1-rc1)

On Tue, Apr 28, 2015 at 01:42:10PM -0700, Andy Lutomirski wrote:
> At some point, I'd like to implement PCID on x86 (if no one beats me
> to it, and this is a low priority for me), which will allow us to skip
> expensive TLB flushes while context switching.  I have no idea whether
> ARM can do something similar.

I talked with Dave about implementing PCID and he thinks that it will be
net loss. TLB entries will live longer and it means we would need to trigger
more IPIs to flash them out when we have to. Cost of IPIs will be higher
than benifit from hot TLB after context switch.

Do you have different expectations?

-- 
 Kirill A. Shutemov
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