From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Srivatsa S. Bhat" Subject: Re: [PATCH v2 38/45] MIPS: Use get/put_online_cpus_atomic() to prevent CPU offline Date: Thu, 27 Jun 2013 12:38:31 +0530 Message-ID: <51CBE4EF.5040302@linux.vnet.ibm.com> References: <20130625202452.16593.22810.stgit@srivatsabhat.in.ibm.com> <20130625203257.16593.15358.stgit@srivatsabhat.in.ibm.com> <20130626133912.GA4559@linux-mips.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: tglx@linutronix.de, peterz@infradead.org, tj@kernel.org, oleg@redhat.com, paulmck@linux.vnet.ibm.com, rusty@rustcorp.com.au, mingo@kernel.org, akpm@linux-foundation.org, namhyung@kernel.org, walken@google.com, vincent.guittot@linaro.org, laijs@cn.fujitsu.com, rostedt@goodmis.org, wangyun@linux.vnet.ibm.com, xiaoguangrong@linux.vnet.ibm.com, sbw@mit.edu, fweisbec@gmail.com, zhong@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com, linux-pm@vger.kernel.org, linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, David Daney , Yong Zhang , Sanjay Lal , "Steven J. Hill" , John Crispin , Florian Fainelli , linux-mips@linux-mips.org To: Ralf Baechle Return-path: In-Reply-To: <20130626133912.GA4559@linux-mips.org> Sender: linux-arch-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 06/26/2013 07:09 PM, Ralf Baechle wrote: > On Wed, Jun 26, 2013 at 02:02:57AM +0530, Srivatsa S. Bhat wrote: > >> Once stop_machine() is gone from the CPU offline path, we won't be able >> to depend on disabling preemption to prevent CPUs from going offline >> from under us. >> >> Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going >> offline, while invoking from atomic context. > > I think the same change also needs to be applied to r4k_on_each_cpu() in > arch/mips/mm/c-r4k.c which currently looks like: > > static inline void r4k_on_each_cpu(void (*func) (void *info), void *info) > { > preempt_disable(); > > #if !defined(CONFIG_MIPS_MT_SMP) && !defined(CONFIG_MIPS_MT_SMTC) > smp_call_function(func, info, 1); > #endif > func(info); > preempt_enable(); > } > Thanks for pointing this out! I'll include changes to this code in my next version. Regards, Srivatsa S. Bhat > This is a slightly specialized version of on_each_cpu() which only calls > out to other CPUs in actual multi-core environments and also - unlike > on_each_cpu() doesn't disable interrupts for the sake of better > interrupt latencies. > > Which reminds me ... > > Andrew, I was wondering why did 78eef01b0fae087c5fadbd85dd4fe2918c3a015f > [[PATCH] on_each_cpu(): disable local interrupts] disable interrupts? > The log is: > > ----- snip ----- > When on_each_cpu() runs the callback on other CPUs, it runs with local > interrupts disabled. So we should run the function with local interrupts > disabled on this CPU, too. > > And do the same for UP, so the callback is run in the same environment on bo > UP and SMP. (strictly it should do preempt_disable() too, but I think > local_irq_disable is sufficiently equivalent). > [...] > ----- snip ----- > > I'm not entirely convinced the symmetry between UP and SMP environments is > really worth it. Would anybody mind removing the local_irq_disable() ... > local_irq_enable() from on_each_cpu()? >