From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTP id 5BA0FDDD04 for ; Fri, 6 Apr 2007 09:04:11 +1000 (EST) Subject: Re: Questions about porting perfmon2 to powerpc From: Benjamin Herrenschmidt To: Kevin Corry In-Reply-To: <200704051455.34600.kevcorry@us.ibm.com> References: <200704051455.34600.kevcorry@us.ibm.com> Content-Type: text/plain Date: Fri, 06 Apr 2007 09:04:02 +1000 Message-Id: <1175814243.30879.146.camel@localhost.localdomain> Mime-Version: 1.0 Cc: linuxppc-dev@ozlabs.org, LKML , Carl Love List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, 2007-04-05 at 14:55 -0500, Kevin Corry wrote: > Hello, > > Carl Love and I have been working on getting the latest perfmon2 patches > (http://perfmon2.sourceforge.net/) working on Cell, and on powerpc in > general. We've come up with some powerpc-specific questions and we're hoping > to get some opinions from the powerpc kernel developers. > > First, the stock 2.6.20 kernel has a prototype in include/linux/smp.h for a > function called smp_call_function_single(). However, this routine is only > implemented on i386, x86_64, ia64, and mips. Perfmon2 apparently needs to > call this to run a function on a specific CPU. Powerpc provides an > smp_call_function() routine to run a function on all active CPUs, so I used > that as a basis to add an smp_call_function_single() routine. I've included > the patch below and was wondering if it looked like a sane approach. We should do better... it will require some backend work for the various supported PICs though. I've always wanted to look into doing a smp_call_function_cpumask in fact :-) > Next, we ran into a problem related to Perfmon2 initialization and sysfs. The > problem turned out to be that the powerpc version of topology_init() is > defined as an __initcall() routine, but Perfmon2's initialization is done as > a subsys_initcall() routine. Thus, Perfmon2 tries to initialize its sysfs > information before some of the powerpc cpu information has been initialized. > However, on all other architectures, topology_init() is defined as a > subsys_initcall() routine, so this problem was not seen on any other > platforms. Changing the powerpc version of topology_init() to a > subsys_initcall() seems to have fixed the bug. However, I'm not sure if that > is going to cause problems elsewhere in the powerpc code. I've included the > patch below (after the smp-call-function-single patch). Does anyone know if > this change is safe, or if there was a specific reason that topology_init() > was left as an __initcall() on powerpc? It would make sense to follow what other archs do. Note that if both perfmon and topology_init are subsys_initcall, that is on the same level, it's still a bit hairy to expect one to be called before the other... Ben.