From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765992AbZFOUFQ (ORCPT ); Mon, 15 Jun 2009 16:05:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757560AbZFOUFE (ORCPT ); Mon, 15 Jun 2009 16:05:04 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:55531 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756815AbZFOUFD (ORCPT ); Mon, 15 Jun 2009 16:05:03 -0400 Date: Mon, 15 Jun 2009 13:04:02 -0700 (PDT) From: Linus Torvalds X-X-Sender: torvalds@localhost.localdomain To: Ingo Molnar cc: Mathieu Desnoyers , mingo@redhat.com, hpa@zytor.com, paulus@samba.org, acme@redhat.com, linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl, penberg@cs.helsinki.fi, vegard.nossum@gmail.com, efault@gmx.de, jeremy@goop.org, npiggin@suse.de, tglx@linutronix.de, linux-tip-commits@vger.kernel.org Subject: Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods In-Reply-To: <20090615194344.GA12554@elte.hu> Message-ID: References: <20090615171845.GA7664@elte.hu> <20090615180527.GB4201@Krystal> <20090615183649.GA16999@elte.hu> <20090615194344.GA12554@elte.hu> User-Agent: Alpine 2.01 (LFD 1184 2008-12-16) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 15 Jun 2009, Ingo Molnar wrote: > > Well i guess it depends. For server apps it is true - syscalls are a > lot more dominant, MMs are long-running so any startup cost gets > amortized and pagefaults are avoided. > > For something like a kernel build we have 7 times as many pagefaults > as syscalls: Ingo - calm down. This is not about page faults. This is purely about taps FROM KERNEL SPACE. Yes, for the kernel build we have 7 times as many page faults as system calls, BUT I BET 99.9% of them are from user mode! The whole "open-code iret" only works for exceptions that happened in kernel mode. That's a _vanishingly_ small number (outside of device interrupts that happen during idle). Linus