linux-kernel - Re: [PATCH v7 8/8] x86/tlb: just do tlb flush on one of siblings of SMT

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Date:	Thu, 24 May 2012 15:23:31 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andrew Lutomirski <luto@....edu>
Cc:	Jan Beulich <JBeulich@...e.com>, Alex Shi <alex.shi@...el.com>,
	borislav.petkov@....com, arnd@...db.de, akinobu.mita@...il.com,
	eric.dumazet@...il.com, fweisbec@...il.com, rostedt@...dmis.org,
	hughd@...gle.com, jeremy@...p.org, len.brown@...el.com,
	tony.luck@...el.com, yongjie.ren@...el.com,
	kamezawa.hiroyu@...fujitsu.com, seto.hidetoshi@...fujitsu.com,
	penberg@...nel.org, yinghai@...nel.org, tglx@...utronix.de,
	akpm@...ux-foundation.org, ak@...ux.intel.com, avi@...hat.com,
	dhowells@...hat.com, mingo@...hat.com, riel@...hat.com,
	cpw@....com, steiner@....com, linux-kernel@...r.kernel.org,
	viro@...iv.linux.org.uk, hpa@...or.com,
	Arjan Van De Ven <arjan@...ux.intel.com>
Subject: Re: [PATCH v7 8/8] x86/tlb: just do tlb flush on one of siblings
 of SMT

On Thu, 2012-05-24 at 06:19 -0700, Andrew Lutomirski wrote:
> 
> A decent heuristic might be to prefer idle SMT siblings for TLB
> invalidation.  I don't know what effect that would have on power
> consumption (it would be rather bad if idling one SMT thread while the
> other one is busy saves much power). 

Right, I've never really understood how C-states and SMT go together.
Arjan recently implied waking a thread sibling from C-state was
'expensive' which on first thought seems daft, the core is running
already.



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