Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261610AbVA3ANW (ORCPT ); Sat, 29 Jan 2005 19:13:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261616AbVA3ANW (ORCPT ); Sat, 29 Jan 2005 19:13:22 -0500 Received: from quark.didntduck.org ([69.55.226.66]:62955 "EHLO quark.didntduck.org") by vger.kernel.org with ESMTP id S261610AbVA3ANQ (ORCPT ); Sat, 29 Jan 2005 19:13:16 -0500 Message-ID: <41FC2693.6060601@didntduck.org> Date: Sat, 29 Jan 2005 19:13:07 -0500 From: Brian Gerst User-Agent: Mozilla Thunderbird (X11/20041216) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Jesper Juhl CC: "Paul `Rusty' Russell" , linux-kernel Subject: Re: [PATCH] micro optimization in kernel/params.c; don't call to_module_kobject before we really have to. References: In-Reply-To: Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2220 Lines: 63 Jesper Juhl wrote: > In kernel/params.c::module_attr_show and > kernel/params.c::module_attr_store we call to_module_kobject() and save > the result in a local variable right before a conditional statement that > does not depend on the call to to_module_kobject() and may cause the > function to return. If the function returns before we use the result of > to_module_kobject() then the call is just a waste of time. > The patch moves the call to to_module_kobject() down just before it is > actually used, thus we save a call to the function in a few cases. I doubt > this is in any way measurable, but I see no reason to not move the call - > it should be an infinitesimal improvement with no ill sideeffects. > Please consider applying. > > > Signed-off-by: Jesper Juhl > > diff -up linux-2.6.11-rc2-bk7-orig/kernel/params.c linux-2.6.11-rc2-bk7/kernel/params.c > --- linux-2.6.11-rc2-bk7-orig/kernel/params.c 2005-01-29 23:54:53.000000000 +0100 > +++ linux-2.6.11-rc2-bk7/kernel/params.c 2005-01-30 00:27:08.000000000 +0100 > @@ -625,11 +625,12 @@ static ssize_t module_attr_show(struct k > int ret; > > attribute = to_module_attr(attr); > - mk = to_module_kobject(kobj); > > if (!attribute->show) > return -EPERM; > > + mk = to_module_kobject(kobj); > + > if (!try_module_get(mk->mod)) > return -ENODEV; > > @@ -649,11 +650,12 @@ static ssize_t module_attr_store(struct > int ret; > > attribute = to_module_attr(attr); > - mk = to_module_kobject(kobj); > > if (!attribute->store) > return -EPERM; > > + mk = to_module_kobject(kobj); > + > if (!try_module_get(mk->mod)) > return -ENODEV; > > > > I'd bet that the compiler already reorders the assignment since there is no side effect to to_module_kobject(). Even with a patch like this you can't control exactly when the assignment is done. There may not even be an assignment, since mk is a constant offset of kobj. -- Brian Gerst - 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/