linux-kernel - Re: [RFC][PATCH 00/26] sched/numa

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Date:	Mon, 2 Apr 2012 19:54:46 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mike Galbraith <efault@....de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Dan Smith <danms@...ibm.com>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC][PATCH 00/26] sched/numa

Hi Rik,

On Wed, Mar 21, 2012 at 12:18 AM, Rik van Riel<riel@...hat.com>  wrote:
>>> I suspect Java and other runtimes may have issues where
>>> they simply do not know which thread will end up using
>>> which objects from the heap heavily.

On 04/02/2012 12:34 PM, Pekka Enberg wrote:
>> What kind of JVM workloads are you thinking of? Modern GCs use
>> thread-local allocation for performance reasons so I'd assume that
>> most of accesses are on local node.

On Mon, Apr 2, 2012 at 7:55 PM, Rik van Riel <riel@...hat.com> wrote:
> Yes, the use thread-local allocation.
>
> However, I suspect that after the memory has been allocated
> locally, it may quite often end up with another thread for
> further processing...

Do you have any specific workloads in mind? My experience makes me
assume the opposite for common JVM server workloads. (And yes, I'm
hand-waving here, I have no data to back that up.)

On Mon, Apr 2, 2012 at 7:55 PM, Rik van Riel <riel@...hat.com> wrote:
> The JVM doing the right thing only helps so much, when the
> Java program has no way to know about underlying things,
> or influence how the threads get scheduled on the JVM.
>
> Allowing us to discover which threads are accessing the
> same data, and figuring out what data each thread uses,
> could be useful for NUMA placement...

Sure, it's probably going to help for the kinds of workloads you're
describing. I'm just wondering how typical they are in the real world.

                        Pekka
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