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

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Message-ID: <1337845230.9783.51.camel@laptop>
Date:	Thu, 24 May 2012 09:40:30 +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
Subject: Re: [PATCH v7 8/8] x86/tlb: just do tlb flush on one of siblings
 of SMT

On Wed, 2012-05-23 at 18:46 -0700, Andrew Lutomirski wrote:
> On Wed, May 23, 2012 at 10:15 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Wed, 2012-05-23 at 19:09 +0200, Peter Zijlstra wrote:
> >> > There is no comment or anything else indicating that this is
> >> > suitable for dual-thread CPUs only - when there are more than
> >> > 2 threads per core, the intended effect won't be achieved.
> >>
> >> Why would that be? Won't higher thread count still share the same
> >> resources just more so?
> >
> > Ah, I see, you're saying his code is buggy for >2 threads. Agreed.
> >
> 
> An evil knob to statically choose which SMT sibling gets the interrupt
> would be nice.  Then my compute-intensive thread could be (mostly)
> unaffected by the other thread on a different core that calls munmap
> frequently.

Just make sure the two workloads never share a core and this should
already happen since TLB invalidates are only broadcast to the mm
cpumask.

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