Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752515Ab0KXPnS (ORCPT ); Wed, 24 Nov 2010 10:43:18 -0500 Received: from mx1.redhat.com ([209.132.183.28]:21925 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750868Ab0KXPnR (ORCPT ); Wed, 24 Nov 2010 10:43:17 -0500 Date: Wed, 24 Nov 2010 10:42:01 -0500 From: Jason Baron To: Peter Zijlstra 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 Subject: Re: [PATCH 1/3] jump label: add enabled/disabled state to jump label key entries Message-ID: <20101124154200.GD2815@redhat.com> References: <1290586809.2072.424.camel@laptop> <20101124145401.GA2815@redhat.com> <1290611478.2072.482.camel@laptop> <20101124151936.GB2815@redhat.com> <1290612245.2072.486.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1290612245.2072.486.camel@laptop> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2159 Lines: 66 On Wed, Nov 24, 2010 at 04:24:05PM +0100, Peter Zijlstra wrote: > 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. > > is this really true? The powerpc implementation uses patch_instruction(): arch/powerpc/lib/code-patching.c: void patch_instruction(unsigned int *addr, unsigned int instr) { *addr = instr; asm ("dcbst 0, %0; sync; icbi 0,%0; sync; isync" : : "r" (addr)); } And sparc does uses flushi(): include/asm/system_64.h: #define flushi(addr) __asm__ __volatile__ ("flush %0" : : "r" (addr) : "memory") thanks, -Jason -- 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/