Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757712Ab3CULhG (ORCPT ); Thu, 21 Mar 2013 07:37:06 -0400 Received: from service87.mimecast.com ([91.220.42.44]:39872 "EHLO service87.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753537Ab3CULhD convert rfc822-to-8bit (ORCPT ); Thu, 21 Mar 2013 07:37:03 -0400 Message-ID: <514AF095.5060802@arm.com> Date: Thu, 21 Mar 2013 11:35:49 +0000 From: Marc Zyngier User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130221 Thunderbird/17.0.3 MIME-Version: 1.0 To: Mark Rutland CC: Rob Herring , Simon Horman , Kukjin Kim , Russell King , Arnd Bergmann , "linux-sh@vger.kernel.org" , Tony Lindgren , Catalin Marinas , Magnus Damm , "linux-kernel@vger.kernel.org" , "rob.herring@calxeda.com" , "linux-samsung-soc@vger.kernel.org" , John Stultz , Will Deacon , Thomas Gleixner , "linux-omap@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH] ARM: convert arm/arm64 arch timer to use CLKSRC_OF init References: <1363818875-15978-1-git-send-email-robherring2@gmail.com> <20130321110646.GE15279@e106331-lin.cambridge.arm.com> In-Reply-To: <20130321110646.GE15279@e106331-lin.cambridge.arm.com> X-Enigmail-Version: 1.4.6 X-OriginalArrivalTime: 21 Mar 2013 11:35:51.0507 (UTC) FILETIME=[3DA4A230:01CE2628] X-MC-Unique: 113032111355115601 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4166 Lines: 111 On 21/03/13 11:06, Mark Rutland wrote: > Hi Rob, > > (adding Marc to Cc as he may have comments). > > On Wed, Mar 20, 2013 at 10:34:35PM +0000, Rob Herring wrote: >> From: Rob Herring >> >> This converts arm and arm64 to use CLKSRC_OF DT based initialization for >> the arch timer. A new function arch_timer_arch_init is added to allow for >> arch specific setup. >> >> This has a side effect of enabling sched_clock on omap5 and exynos5. There >> should not be any reason not to use the arch timers for sched_clock. > > Nice! I was just about to post a (slightly updated) version of Thomas Abraham's > arch_timer clocksource_of_init patch, but this seems much more comprehensive. > > I have some other arch_timer patches which may clash, but they could be rebased > atop of this. > >> >> Signed-off-by: Rob Herring >> Cc: Russell King >> Cc: Kukjin Kim >> Cc: Tony Lindgren >> Cc: Simon Horman >> Cc: Magnus Damm >> Cc: Catalin Marinas >> Cc: Will Deacon >> Cc: John Stultz >> Cc: Thomas Gleixner >> Cc: linux-samsung-soc@vger.kernel.org >> Cc: linux-omap@vger.kernel.org >> Cc: linux-sh@vger.kernel.org >> --- >> This is dependent on my CLKSRC_OF clean-up in arm-soc, my 64-bit sched_clock >> support series, and Arnd's default machine descriptor patch (for default >> clocksource_of_init call). This is only compile tested on arm. >> >> The full series (including sp804 work) is available here: >> git://sources.calxeda.com/kernel/linux.git arm-timers >> >> Rob >> > > [...] > >> diff --git a/arch/arm/mach-vexpress/v2m.c b/arch/arm/mach-vexpress/v2m.c >> index d0ad789..6215717 100644 >> --- a/arch/arm/mach-vexpress/v2m.c >> +++ b/arch/arm/mach-vexpress/v2m.c >> @@ -1,6 +1,7 @@ >> /* >> * Versatile Express V2M Motherboard Support >> */ >> +#include >> #include >> #include >> #include >> @@ -23,7 +24,6 @@ >> #include >> #include >> >> -#include >> #include >> #include >> #include >> @@ -446,10 +446,7 @@ static void __init v2m_dt_timer_init(void) >> irq_of_parse_and_map(node, 0)); >> } >> >> - arch_timer_of_register(); >> - >> - if (arch_timer_sched_clock_init() != 0) >> - versatile_sched_clock_init(vexpress_get_24mhz_clock_base(), >> + versatile_sched_clock_init(vexpress_get_24mhz_clock_base(), >> 24000000); >> } >> > > On TC2 this series leads to using the vexpress 24MHz clock as the sched clock > in preference to the architected timer: > > Architected local timer running at 24.00MHz (virt). > Switching to timer-based delay loop > Registered arch_counter_get_cntvct+0x0/0x14 as sched_clock source > sched_clock: 32 bits at 24MHz, resolution 41ns, wraps every 178956ms > Registered versatile_read_sched_clock+0x0/0x28 as sched_clock source > > As they both have the same frequency, neither overrides the other, and > whichever gets registered last is used as the sched_clock. As accesses to the > architected timer are going to have a much lower overhead, this isn't very nice > (and it could be better to use it even if it had a lower frequency). Indeed. And if I look at it with my KVM hat on, it is even worse (the guest will exit all the way to platform emulation in userspace on each sched_clock read - a sure performance killer). Of course, emulating a VE is not the best option, but that's all we have so far when using QEMU as platform emulation. M. -- Jazz is not dead. It just smells funny... -- 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/