From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935423Ab3FTIn0 (ORCPT ); Thu, 20 Jun 2013 04:43:26 -0400 Received: from intranet.asianux.com ([58.214.24.6]:20004 "EHLO intranet.asianux.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935353Ab3FTInX (ORCPT ); Thu, 20 Jun 2013 04:43:23 -0400 X-Spam-Score: -100.8 Message-ID: <51C2C077.2050900@asianux.com> Date: Thu, 20 Jun 2013 16:42:31 +0800 From: Chen Gang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 MIME-Version: 1.0 To: Thomas Gleixner CC: "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] kernel/timer.c: using spin_lock_irqsave instead of spin_lock + local_irq_save, especially when CONFIG_LOCKDEP not defined References: <51C11E83.8030902@asianux.com> <51C17D01.2060208@asianux.com> <51C182EE.5070500@asianux.com> <51C28193.3080106@asianux.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/20/2013 03:36 PM, Thomas Gleixner wrote: > On Thu, 20 Jun 2013, Chen Gang wrote: >> > On 06/19/2013 06:49 PM, Thomas Gleixner wrote: >>> > > We must do this because some architectures implement >>> > > do_raw_spin_lock_flags() in the following way: >>> > > >>> > > do_raw_spin_lock_flags(l, flags) >>> > > { >>> > > while (!arch_spin_trylock(l)) { >>> > > if (!irq_disabled_flags(flags)) { >>> > > arch_irq_restore(flags); >>> > > cpu_relax(); >>> > > arch_irq_disable(); >>> > > } >>> > > } >>> > > } >>> > > >> > >> > For mn10300 and sparc64 (not space32), it doesn't like your demo above. > Sigh. You're an sparc64 and mn10300 assembler expert, right? > No, do you mean: "only the related expert can discuss about it" ? >> > For powerpc and s390, it seems your demo above (although not quite >> > precious) > It does not matter at all whether the code is implemented exactly that > way. What matters is that the semantics are the same. > >> > For x86 and parisc, it like your demo above. > For parisc, yes. > > For x86, no. > > static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock, > unsigned long flags) > { > arch_spin_lock(lock); > } > That is one of x86 implementation, not all (please see xen implementation) >>> > > And again. Both are semantically the same. >>> > > >> > >> > I am not quite sure about mn10300 and sparc64. >> > >> > Could you be sure about it ? > I am sure, because I can read _and_ understand the asm code. > Are you expert of them ? ;-) But whether you stick to or not, I do not care about it. >> > At least, for mn10300 and sparc64, they have no duty to make sure of >> > our using ways to be correct. > You think that architectures can implement these functions as they > want and see fit? No, they can't otherwise their kernel would not work > at all. Again the semantics are what we care about, not the > implementation. And it's totally irrelevant whether its implemented in > C or in assembler. > Of cause, it is independent with language. >>> > > spin_lock_irqsave() semantics are: >>> > > >>> > > The function returns with the lock acquired, interrupts and preemption >>> > > disabled. Both variants do that. >>> > > >>> > > The internal details whether an architecture reenables interrupts >>> > > while spinning on a contended lock or not are completely irrelevant >>> > > and do not affect the correctness of the code. >> > >> > For API definition, it has no duty to make it correct if the user call >> > them with informal ways, especially, the implementation is related with >> > various architectures. > Nonsense. > The word 'Nonsense' seems not quite polite. ;-) At least, when some one see this usage below: spin_lock_irqsave(&l1, flags); spin_unlock(&l1); spin_lock(&l2); spin_unlock_irqrestore(&l2, flags); most of them will be amazing. Thanks. -- Chen Gang Asianux Corporation