Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753700Ab2KPWhU (ORCPT ); Fri, 16 Nov 2012 17:37:20 -0500 Received: from terminus.zytor.com ([198.137.202.10]:36954 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753450Ab2KPWhT (ORCPT ); Fri, 16 Nov 2012 17:37:19 -0500 User-Agent: K-9 Mail for Android In-Reply-To: <1353104456.7586.27.camel@gandalf.local.home> References: <20121116214644.8521.79072.stgit@ahduyck-cp1.jf.intel.com> <20121116215718.8521.24026.stgit@ahduyck-cp1.jf.intel.com> <1353104456.7586.27.camel@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: Re: [PATCH v4 6/8] x86/ftrace: Use __pa_symbol instead of __pa on C visible symbols From: "H. Peter Anvin" Date: Fri, 16 Nov 2012 14:25:28 -0800 To: Steven Rostedt , Alexander Duyck CC: tglx@linutronix.de, mingo@redhat.com, andi@firstfloor.org, Frederic Weisbecker , x86@kernel.org, linux-kernel@vger.kernel.org Message-ID: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2305 Lines: 67 It is a performance improvement. Steven Rostedt wrote: >On Fri, 2012-11-16 at 13:57 -0800, Alexander Duyck wrote: >> Instead of using __pa which is meant to be a general function for >converting >> virtual addresses to physical addresses we can use __pa_symbol which >is the >> preferred way of decoding kernel text virtual addresses to physical >addresses. >> >> In this case we are not directly converting C visible symbols however >if we >> know that the instruction pointer is somewhere between _text and >_etext we >> know that we are going to be translating an address form the kernel >text >> space. > >Can I ask what the purpose of this is? I'm a little skeptical of a >change that is just "the preferred way". > >Was there some bug that this fixes? > >-- Steve > >> >> Cc: Steven Rostedt >> Cc: Frederic Weisbecker >> Signed-off-by: Alexander Duyck >> --- >> arch/x86/kernel/ftrace.c | 4 ++-- >> 1 files changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c >> index 1d41402..42a392a 100644 >> --- a/arch/x86/kernel/ftrace.c >> +++ b/arch/x86/kernel/ftrace.c >> @@ -89,7 +89,7 @@ do_ftrace_mod_code(unsigned long ip, const void >*new_code) >> * kernel identity mapping to modify code. >> */ >> if (within(ip, (unsigned long)_text, (unsigned long)_etext)) >> - ip = (unsigned long)__va(__pa(ip)); >> + ip = (unsigned long)__va(__pa_symbol(ip)); >> >> return probe_kernel_write((void *)ip, new_code, MCOUNT_INSN_SIZE); >> } >> @@ -279,7 +279,7 @@ static int ftrace_write(unsigned long ip, const >char *val, int size) >> * kernel identity mapping to modify code. >> */ >> if (within(ip, (unsigned long)_text, (unsigned long)_etext)) >> - ip = (unsigned long)__va(__pa(ip)); >> + ip = (unsigned long)__va(__pa_symbol(ip)); >> >> return probe_kernel_write((void *)ip, val, size); >> } -- Sent from my mobile phone. Please excuse brevity and lack of formatting. -- 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/