From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752607Ab1LCXOk (ORCPT ); Sat, 3 Dec 2011 18:14:40 -0500 Received: from e5.ny.us.ibm.com ([32.97.182.145]:35826 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751650Ab1LCXOi (ORCPT ); Sat, 3 Dec 2011 18:14:38 -0500 Date: Sat, 3 Dec 2011 15:14:29 -0800 From: "Paul E. McKenney" To: Josh Triplett Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, patches@linaro.org, "Paul E. McKenney" Subject: Re: [PATCH RFC tip/core/rcu 6/7] driver-core/cpu: Add cpu_is_hotpluggable() for rcutorture error analysis Message-ID: <20111203231429.GB18961@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20111203183417.GA18914@linux.vnet.ibm.com> <1322937282-19846-6-git-send-email-paulmck@linux.vnet.ibm.com> <20111203210650.GA17377@leaf> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111203210650.GA17377@leaf> User-Agent: Mutt/1.5.20 (2009-06-14) x-cbid: 11120323-5930-0000-0000-000002DBDD1B Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Dec 03, 2011 at 01:06:50PM -0800, Josh Triplett wrote: > On Sat, Dec 03, 2011 at 10:34:41AM -0800, Paul E. McKenney wrote: > > The rcutorture test now can automatically exercise CPU hotplug and > > collect success statistics, which can be correlated with other rcutorture > > activity. This permits rcutorture to completely exercise RCU regardless > > of what sort of userspace and filesystem layout is in use. Unfortunately, > > rcutorture is happy to attempt to offline CPUs that cannot be offlined, > > for example, CPU 0 in both the x86 and ARM architectures. Although this > > allows rcutorture testing to proceed normally, it confounds attempts at > > error analysis due to the resulting flood of spurious CPU-hotplug errors. > > > > Therefore, this commit creates a cpu_is_hotpluggable() function that > > allows rcutorture to avoid attempting to offline CPUs that are not > > hotpluggable, which in turn allows rcutorture to avoid reporting spurious > > CPU-hotplug errors. Note that this function is EXPORT_SYMBOL_GPL() > > to allow rcutorture to use it when compiled as a kernel module. > > This commit also includes modifications to rcutorture to use this > > new function. > > I'd suggest writing this as a two-patch series: add the API, then use > it. > > I'd also suggest making the more general case for this API, beyond just > rcutorture. > > > --- a/drivers/base/cpu.c > > +++ b/drivers/base/cpu.c > > @@ -23,6 +23,7 @@ struct sysdev_class cpu_sysdev_class = { > > EXPORT_SYMBOL(cpu_sysdev_class); > > > > static DEFINE_PER_CPU(struct sys_device *, cpu_sys_devices); > > +static DEFINE_PER_CPU(bool, is_hotpluggable); > [...] > > @@ -224,8 +226,10 @@ int __cpuinit register_cpu(struct cpu *cpu, int num) > > > > error = sysdev_register(&cpu->sysdev); > > > > - if (!error && cpu->hotpluggable) > > + if (!error && cpu->hotpluggable) { > > register_cpu_control(cpu); > > + per_cpu(is_hotpluggable, num) = 1; > > + } > > This information already exists in the ->hotpluggable field of "struct > cpu". I'd suggest an alternate approach (included as a patch below), > which avoids the need to add a new per_cpu property redundant with > ->hotpluggable. I do like your patch better, as it is smaller, less intrusive, and makes better use of existing facilities. I have therefore replaced mine with it. I also created a separate patch containing the rcutorture modifications from my original. > Note that you can get to the patch below via "git am --scissors", or > just by copy/pasting it. Very cool -- wasn't aware of --scissors before. ;-) Thanx, Paul > ---8<--- > From: Josh Triplett > Subject: [PATCH] driver-core/cpu: Expose hotpluggability to the rest of the kernel > > When architectures register CPUs, they indicate whether the CPU allows > hotplugging; notably, x86 and ARM don't allow hotplugging CPU 0. > Userspace can easily query the hotpluggability of a CPU via sysfs; > however, the kernel has no convenient way of accessing that property in > an architecture-independent way. While the kernel can simply try it and > see, some code needs to distinguish between "hotplug failed" and > "hotplug has no hope of working on this CPU"; for example, rcutorture's > CPU hotplug tests want to avoid drowning out real hotplug failures with > expected failures. > > Expose this property via a new cpu_is_hotpluggable function, so that the > rest of the kernel can access it in an architecture-independent way. > > Signed-off-by: Josh Triplett > --- > drivers/base/cpu.c | 7 +++++++ > include/linux/cpu.h | 1 + > 2 files changed, 8 insertions(+), 0 deletions(-) > > diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c > index 251acea..3991502 100644 > --- a/drivers/base/cpu.c > +++ b/drivers/base/cpu.c > @@ -247,6 +247,13 @@ struct sys_device *get_cpu_sysdev(unsigned cpu) > } > EXPORT_SYMBOL_GPL(get_cpu_sysdev); > > +bool cpu_is_hotpluggable(unsigned cpu) > +{ > + struct sys_device *dev = get_cpu_sysdev(cpu); > + return dev && container_of(dev, struct cpu, sysdev)->hotpluggable; > +} > +EXPORT_SYMBOL_GPL(cpu_is_hotpluggable); > + > int __init cpu_dev_init(void) > { > int err; > diff --git a/include/linux/cpu.h b/include/linux/cpu.h > index 6cb60fd..305c263 100644 > --- a/include/linux/cpu.h > +++ b/include/linux/cpu.h > @@ -27,6 +27,7 @@ struct cpu { > > extern int register_cpu(struct cpu *cpu, int num); > extern struct sys_device *get_cpu_sysdev(unsigned cpu); > +extern bool cpu_is_hotpluggable(unsigned cpu); > > extern int cpu_add_sysdev_attr(struct sysdev_attribute *attr); > extern void cpu_remove_sysdev_attr(struct sysdev_attribute *attr); > -- > 1.7.7.3 >