Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752726Ab0KXPYD (ORCPT ); Wed, 24 Nov 2010 10:24:03 -0500 Received: from casper.infradead.org ([85.118.1.10]:40977 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750868Ab0KXPYB convert rfc822-to-8bit (ORCPT ); Wed, 24 Nov 2010 10:24:01 -0500 Subject: Re: [PATCH 1/3] jump label: add enabled/disabled state to jump label key entries From: Peter Zijlstra To: Jason Baron Cc: rostedt@goodmis.org, mingo@elte.hu, mathieu.desnoyers@polymtl.ca, hpa@zytor.com, tglx@linutronix.de, andi@firstfloor.org, roland@redhat.com, rth@redhat.com, masami.hiramatsu.pt@hitachi.com, fweisbec@gmail.com, avi@redhat.com, davem@davemloft.net, sam@ravnborg.org, ddaney@caviumnetworks.com, michael@ellerman.id.au, linux-kernel@vger.kernel.org In-Reply-To: <20101124151936.GB2815@redhat.com> References: <1290586809.2072.424.camel@laptop> <20101124145401.GA2815@redhat.com> <1290611478.2072.482.camel@laptop> <20101124151936.GB2815@redhat.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Wed, 24 Nov 2010 16:24:05 +0100 Message-ID: <1290612245.2072.486.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1591 Lines: 38 On Wed, 2010-11-24 at 10:19 -0500, Jason Baron wrote: > On Wed, Nov 24, 2010 at 04:11:18PM +0100, Peter Zijlstra wrote: > > On Wed, 2010-11-24 at 09:54 -0500, Jason Baron wrote: > > > On Wed, Nov 24, 2010 at 09:20:09AM +0100, Peter Zijlstra wrote: > > > > On Tue, 2010-11-23 at 16:27 -0500, Jason Baron wrote: > > > > > struct hlist_head modules; > > > > > unsigned long key; > > > > > + u32 nr_entries : 31, > > > > > + enabled : 1; > > > > > }; > > > > > > > > I still don't see why you do this, why not simply mandate that the key > > > > is of type atomic_t* and use *key as enabled state? > > > > > > > > > > Because I want to use *key as a pointer directly to 'struct jump_label_entry'. > > > In this way jump_label_enable(), jump_label_disable(), become O(1) operations. > > > That way we don't need any hashing. > > > > But but but, you're doing a friggin stop_machine to poke text, that's > > way more expensive than anything else. > > > > Yes, but other arches do not require stop_machine(). Also, there is work > for x86 to make the code patching happen without stop_machine(). Even without stop machine you're sending IPIs to all CPUs, that's not free either. And I think the only arch where you can do text pokes without cross-cpu synchronization is one that doesn't have SMP support. -- 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/