linux-kernel - Re: [RFC][PATCH 6/8] mm: handle_speculative

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Date:	Fri, 8 Jan 2010 09:52:58 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Christoph Lameter <cl@...ux-foundation.org>
cc:	Peter Zijlstra <peterz@...radead.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Minchan Kim <minchan.kim@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"hugh.dickins" <hugh.dickins@...cali.co.uk>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC][PATCH 6/8] mm: handle_speculative_fault()



On Fri, 8 Jan 2010, Christoph Lameter wrote:
> 
> Can we at least consider a typical standard business server, dual quad
> core hyperthreaded with 16 "cpus"? Cacheline contention will increase
> significantly there.

I bet it won't be a problem. It's when things go cross-socket that they 
suck. So 16 cpu's across two sockets I wouldn't worry about.

> > Because let's face it - if your workload does several million page faults
> > per second, you're just doing something fundamentally _wrong_.
> 
> You may just want to get your app running and its trying to initialize
> its memory in parallel on all threads. Nothing wrong with that.

Umm. That's going to be limited by the memset/memcpy, not the rwlock, I 
bet.

The benchmark in question literally did a single byte write to each page 
in order to show just the kernel component. That really isn't realistic 
for any real load.

			Linus
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