Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932986AbXJRH5W (ORCPT ); Thu, 18 Oct 2007 03:57:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753896AbXJRH5M (ORCPT ); Thu, 18 Oct 2007 03:57:12 -0400 Received: from e31.co.us.ibm.com ([32.97.110.149]:58654 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753112AbXJRH5L (ORCPT ); Thu, 18 Oct 2007 03:57:11 -0400 Date: Thu, 18 Oct 2007 13:27:02 +0530 From: Gautham R Shenoy To: Nathan Lynch Cc: Linus Torvalds , Andrew Morton , linux-kernel@vger.kernel.org, Srivatsa Vaddagiri , Rusty Russel , Dipankar Sarma , Oleg Nesterov , Ingo Molnar , Paul E McKenney Subject: Re: [RFC PATCH 2/4] Rename lock_cpu_hotplug to get_online_cpus Message-ID: <20071018075702.GB15281@in.ibm.com> Reply-To: ego@in.ibm.com References: <20071016103308.GA9907@in.ibm.com> <20071016103506.GB16570@in.ibm.com> <20071017161308.GD6773@localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071017161308.GD6773@localdomain> User-Agent: Mutt/1.5.12-2006-07-14 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2562 Lines: 74 Hi Nathan, > Hi Gautham- > > Gautham R Shenoy wrote: > > Replace all lock_cpu_hotplug/unlock_cpu_hotplug from the kernel and use > > get_online_cpus and put_online_cpus instead as it highlights > > the refcount semantics in these operations. > > Something other than "get_online_cpus", please? lock_cpu_hotplug() > protects cpu_present_map as well as cpu_online_map. For example, some > of the powerpc code modified in this patch is made a bit less clear > because it is manipulating cpu_present_map, not cpu_online_map. A quick look at the code, and I am wondering why is lock_cpu_hotplug() used there in the first place. It doesn't look like we require any protection against cpus coming up/ going down in the code below, since the cpu-hotplug operation doesn't affect the cpu_present_map. Can't we use another mutex here instead of the cpu_hotplug mutex here ? > > > > Index: linux-2.6.23/arch/powerpc/platforms/pseries/hotplug-cpu.c > > =================================================================== > > --- linux-2.6.23.orig/arch/powerpc/platforms/pseries/hotplug-cpu.c > > +++ linux-2.6.23/arch/powerpc/platforms/pseries/hotplug-cpu.c > > @@ -151,7 +151,7 @@ static int pseries_add_processor(struct > > for (i = 0; i < nthreads; i++) > > cpu_set(i, tmp); > > > > - lock_cpu_hotplug(); > > + get_online_cpus(); > > > > BUG_ON(!cpus_subset(cpu_present_map, cpu_possible_map)); > > > > @@ -188,7 +188,7 @@ static int pseries_add_processor(struct > > } > > err = 0; > > out_unlock: > > - unlock_cpu_hotplug(); > > + put_online_cpus(); > > return err; > > } > > > > @@ -209,7 +209,7 @@ static void pseries_remove_processor(str > > > > nthreads = len / sizeof(u32); > > > > - lock_cpu_hotplug(); > > + get_online_cpus(); > > for (i = 0; i < nthreads; i++) { > > for_each_present_cpu(cpu) { > > if (get_hard_smp_processor_id(cpu) != intserv[i]) > > @@ -223,7 +223,7 @@ static void pseries_remove_processor(str > > printk(KERN_WARNING "Could not find cpu to remove " > > "with physical id 0x%x\n", intserv[i]); > > } > > - unlock_cpu_hotplug(); > > + put_online_cpus(); > > } -- Gautham R Shenoy Linux Technology Center IBM India. "Freedom comes with a price tag of responsibility, which is still a bargain, because Freedom is priceless!" - 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/