From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750746AbWDPPel (ORCPT ); Sun, 16 Apr 2006 11:34:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750745AbWDPPek (ORCPT ); Sun, 16 Apr 2006 11:34:40 -0400 Received: from moutng.kundenserver.de ([212.227.126.188]:51661 "EHLO moutng.kundenserver.de") by vger.kernel.org with ESMTP id S1750743AbWDPPej (ORCPT ); Sun, 16 Apr 2006 11:34:39 -0400 From: Arnd Bergmann To: Steven Rostedt Subject: Re: [PATCH 00/05] robust per_cpu allocation for modules Date: Sun, 16 Apr 2006 17:34:18 +0200 User-Agent: KMail/1.9.1 Cc: Paul Mackerras , Nick Piggin , LKML , Andrew Morton , Linus Torvalds , Ingo Molnar , Thomas Gleixner , Andi Kleen , Martin Mares , bjornw@axis.com, schwidefsky@de.ibm.com, benedict.gaster@superh.com, lethal@linux-sh.org, Chris Zankel , Marc Gauthier , Joe Taylor , David Mosberger-Tang , rth@twiddle.net, spyro@f2s.com, starvik@axis.com, tony.luck@intel.com, linux-ia64@vger.kernel.org, ralf@linux-mips.org, linux-mips@linux-mips.org, grundler@parisc-linux.org, parisc-linux@parisc-linux.org, linuxppc-dev@ozlabs.org, linux390@de.ibm.com, davem@davemloft.net, rusty@rustcorp.com.au References: <1145049535.1336.128.camel@localhost.localdomain> <17473.60411.690686.714791@cargo.ozlabs.ibm.com> <1145194804.27407.103.camel@localhost.localdomain> In-Reply-To: <1145194804.27407.103.camel@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200604161734.20256.arnd@arndb.de> X-Provags-ID: kundenserver.de abuse@kundenserver.de login:c48f057754fc1b1a557605ab9fa6da41 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sunday 16 April 2006 15:40, Steven Rostedt wrote: > I'll think more about this, but maybe someone else has some crazy ideas > that can find a solution to this that is both fast and robust. Ok, you asked for a crazy idea, you're going to get it ;-) You could take a fixed range from the vmalloc area (e.g. 1MB per cpu) and use that to remap pages on demand when you need per cpu data. #define PER_CPU_BASE 0xe000000000000000UL /* arch dependant */ #define PER_CPU_SHIFT 0x100000UL #define __per_cpu_offset(__cpu) (PER_CPU_BASE + PER_CPU_STRIDE * (__cpu)) #define per_cpu(var, cpu) (*RELOC_HIDE(&per_cpu__##var, __per_cpu_offset(cpu))) #define __get_cpu_var(var) per_cpu(var, smp_processor_id()) This is a lot like the current sparc64 implementation already is. The tricky part here is the remapping of pages. You'd need to alloc_pages_node() new pages whenever the already reserved space is not enough for the module you want to load and then map_vm_area() them into the space reserved for them. Advantages of this solution are: - no dependant load access for per_cpu() - might be flexible enough to implement a faster per_cpu_ptr() - can be combined with ia64-style per-cpu remapping Disadvantages are: - you can't use huge tlbs for mapping per cpu data like the regular linear mapping -> may be slower on some archs - does not work in real mode, so percpu data can't be used inside exception handlers on some architectures. - memory consumption is rather high when PAGE_SIZE is large Arnd <><