Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759958Ab3CGXfv (ORCPT ); Thu, 7 Mar 2013 18:35:51 -0500 Received: from mail-lb0-f178.google.com ([209.85.217.178]:45285 "EHLO mail-lb0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752993Ab3CGXft convert rfc822-to-8bit (ORCPT ); Thu, 7 Mar 2013 18:35:49 -0500 MIME-Version: 1.0 In-Reply-To: <20130211143529.GB2749@pd.tnic> References: <1357610913-1080-1-git-send-email-fweisbec@gmail.com> <1357610913-1080-8-git-send-email-fweisbec@gmail.com> <20130211143529.GB2749@pd.tnic> Date: Fri, 8 Mar 2013 00:35:47 +0100 Message-ID: Subject: Re: [PATCH 07/33] nohz: Basic full dynticks interface From: Frederic Weisbecker To: Borislav Petkov Cc: Frederic Weisbecker , LKML , Alessio Igor Bogani , Andrew Morton , Chris Metcalf , Christoph Lameter , Geoff Levand , Gilad Ben Yossef , Hakan Akkan , Ingo Molnar , Li Zhong , Namhyung Kim , "Paul E. McKenney" , Paul Gortmaker , Peter Zijlstra , Steven Rostedt , Thomas Gleixner 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: 2919 Lines: 86 2013/2/11 Borislav Petkov : > On Tue, Jan 08, 2013 at 03:08:07AM +0100, Frederic Weisbecker wrote: > > [ ? ] > >> diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig >> index 8601f0d..dc6381d 100644 >> --- a/kernel/time/Kconfig >> +++ b/kernel/time/Kconfig >> @@ -70,6 +70,15 @@ config NO_HZ >> only trigger on an as-needed basis both when the system is >> busy and when the system is idle. >> >> +config NO_HZ_FULL >> + bool "Full tickless system" > > I think you want to say here "Almost-completely tickless system". > "Almost" because of that one CPU outside of the range :-) I think that "Full dynticks system" would express well what happens? > >> + depends on NO_HZ && RCU_USER_QS && VIRT_CPU_ACCOUNTING_GEN && RCU_NOCB_CPU && SMP >> + select CONTEXT_TRACKING_FORCE >> + help >> + Try to be tickless everywhere, not just in idle. (You need >> + to fill up the full_nohz_mask boot parameter). >> + >> + >> config HIGH_RES_TIMERS >> bool "High Resolution Timer Support" >> depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS >> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c >> index 314b9ee..494a2aa 100644 >> --- a/kernel/time/tick-sched.c >> +++ b/kernel/time/tick-sched.c >> @@ -142,6 +142,29 @@ static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs) >> profile_tick(CPU_PROFILING); >> } >> >> +#ifdef CONFIG_NO_HZ_FULL >> +static cpumask_var_t full_nohz_mask; >> +bool have_full_nohz_mask; >> + >> +int tick_nohz_full_cpu(int cpu) >> +{ >> + if (!have_full_nohz_mask) >> + return 0; >> + >> + return cpumask_test_cpu(cpu, full_nohz_mask); >> +} >> + >> +/* Parse the boot-time nohz CPU list from the kernel parameters. */ >> +static int __init tick_nohz_full_setup(char *str) >> +{ >> + alloc_bootmem_cpumask_var(&full_nohz_mask); >> + have_full_nohz_mask = true; >> + cpulist_parse(str, full_nohz_mask); > > Don't you want to check retval of cpulist_parse first here before > assigning have_full_nohz_mask and allocating cpumask var? > > We don't trust userspace, you know. Yeah sure. I was really in draft/laboratory mode until now. But I guess I need to start thinking about such details, since nobody seem to oppose with the whole design. Time to zoom in. > >> + return 1; >> +} >> +__setup("full_nohz=", tick_nohz_full_setup); > > I'd guess this kernel parameter needs to go into > Documentation/kernel-parameters.txt along with a referral to > Documentation/cputopology.txt which explains how to specify cpulists for > n00bs like me :-) Sure, I'll add that on my TODO list. Thanks! -- 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/