Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932777AbZFOSs2 (ORCPT ); Mon, 15 Jun 2009 14:48:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751413AbZFOSsU (ORCPT ); Mon, 15 Jun 2009 14:48:20 -0400 Received: from casper.infradead.org ([85.118.1.10]:60181 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762599AbZFOSsT (ORCPT ); Mon, 15 Jun 2009 14:48:19 -0400 Subject: Re: [tip:perfcounters/core] x86: Add NMI types for kmap_atomic From: Peter Zijlstra To: Ingo Molnar Cc: Hugh Dickins , linux-kernel@vger.kernel.org, mingo@redhat.com, hpa@zytor.com, paulus@samba.org, acme@redhat.com, efault@gmx.de, npiggin@suse.de, tglx@linutronix.de, linux-tip-commits@vger.kernel.org, Linus Torvalds , Andrew Morton In-Reply-To: <20090615184217.GG11248@elte.hu> References: <1245077165.6800.497.camel@laptop> <1245080486.6800.561.camel@laptop> <1245089065.13761.19316.camel@twins> <20090615181555.GA11248@elte.hu> <1245089943.13761.19334.camel@twins> <20090615182549.GD11248@elte.hu> <1245090608.13761.19349.camel@twins> <20090615184217.GG11248@elte.hu> Content-Type: text/plain Date: Mon, 15 Jun 2009 20:47:54 +0200 Message-Id: <1245091674.6741.180.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1425 Lines: 34 On Mon, 2009-06-15 at 20:42 +0200, Ingo Molnar wrote: > * Peter Zijlstra wrote: > > > On Mon, 2009-06-15 at 20:25 +0200, Ingo Molnar wrote: > > > * Peter Zijlstra wrote: > > > > > but ... look at the APIs i propose above. We dont need _any_ > > > 'types'. > > > > > > That type enumeration is basically an open-coded allocator. If we do > > > a _real_ allocator (a balanced stack of atomic kmaps) we dont need > > > any of those indices, and all the potential for mismatch goes away > > > as well - a stack nests trivially with IRQ and NMI and arbitrary > > > other contexts. > > > > You want types because: > > - they encode the intent, and can be verified > > - they help keep track of the max nesting depth > > > > In the proposed implementation all type code basically falls away > > no ! CONFIG_DEBUG_VM, but is kept around for robustness. > > But much of the fragility of the types (and their clumsiness - for > example in highpte ops we have to know at which level of the > pagetables we are, and use the right kind of index) is _precisely_ > because we have the types ... How will you manage the max depth? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/