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Message-ID: <CABeCy1YkEtMnG5CtLhej5w6ywTaO+Rqkr6JWmegfUtEkOobBgg@mail.gmail.com>
Date: Fri, 10 Feb 2012 14:28:08 -0800
From: Venki Pallipadi <venki@...gle.com>
To: Dmitry Antipov <dmitry.antipov@...aro.org>
Cc: linux-kernel@...r.kernel.org,
Russell King <linux@....linux.org.uk>,
Rusty Russell <rusty@...tcorp.com.au>,
Ingo Molnar <mingo@...hat.com>,
Yong Zhang <yong.zhang0@...il.com>, x86@...nel.org,
linux-arm-kernel@...ts.infradead.org, linaro-dev@...ts.linaro.org,
patches@...aro.org
Subject: Re: [PATCH] sched: generalize CONFIG_IRQ_TIME_ACCOUNTING for X86 and ARM
> + noirqtime [X86,ARM] Used to run time disable IRQ_TIME_ACCOUNTING,
> + should give a negligible performance improvement.
Can you reword the above "negligible performance improvement" above to
something
> + noirqtime [X86,ARM] Run time disables IRQ_TIME_ACCOUNTING and
> + eliminates the timestamping on irq/softirq entry/exit.
Otherwise,
Acked-by: Venkatesh Pallipadi <venki@...gle.com>
On Thu, Feb 9, 2012 at 9:25 AM, Dmitry Antipov
<dmitry.antipov@...aro.org> wrote:
> Generalize CONFIG_IRQ_TIME_ACCOUNTING between X86 and
> ARM, move "noirqtime=" option to common debugging code.
> For a bit of backward compatibility, X86-specific option
> "tsc=noirqtime" is preserved, but issues a warning.
>
> Suggested-by: Yong Zhang <yong.zhang0@...il.com>
> Suggested-by: Russell King <rmk+kernel@....linux.org.uk>
> Suggested-by: Venki Pallipadi <venki@...gle.com>
> Signed-off-by: Dmitry Antipov <dmitry.antipov@...aro.org>
> ---
> Documentation/kernel-parameters.txt | 9 +++++----
> arch/arm/kernel/sched_clock.c | 2 ++
> arch/x86/Kconfig | 11 -----------
> arch/x86/kernel/tsc.c | 12 ++++++------
> include/linux/sched.h | 17 ++++++++++-------
> kernel/sched/core.c | 20 +++++++++++---------
> lib/Kconfig.debug | 12 ++++++++++++
> 7 files changed, 46 insertions(+), 37 deletions(-)
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 033d4e6..666d20e 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -1790,6 +1790,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> noirqdebug [X86-32] Disables the code which attempts to detect and
> disable unhandled interrupt sources.
>
> + noirqtime [X86,ARM] Used to run time disable IRQ_TIME_ACCOUNTING,
> + should give a negligible performance improvement.
> +
> no_timer_check [X86,APIC] Disables the code which tests for
> broken timer IRQ sources.
>
> @@ -2636,10 +2639,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> as the stability checks done at bootup. Used to enable
> high-resolution timer mode on older hardware, and in
> virtualized environment.
> - [x86] noirqtime: Do not use TSC to do irq accounting.
> - Used to run time disable IRQ_TIME_ACCOUNTING on any
> - platforms where RDTSC is slow and this accounting
> - can add overhead.
> + [x86] noirqtime: obsoleted by "noirqtime" generic option,
> + see it's documentation for details.
>
> turbografx.map[2|3]= [HW,JOY]
> TurboGraFX parallel port interface
> diff --git a/arch/arm/kernel/sched_clock.c b/arch/arm/kernel/sched_clock.c
> index 5416c7c..30b5f89 100644
> --- a/arch/arm/kernel/sched_clock.c
> +++ b/arch/arm/kernel/sched_clock.c
> @@ -144,6 +144,8 @@ void __init setup_sched_clock(u32 (*read)(void), int bits, unsigned long rate)
> */
> cd.epoch_ns = 0;
>
> + enable_sched_clock_irqtime();
> +
> pr_debug("Registered %pF as sched_clock source\n", read);
> }
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 5bed94e..4759676 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -805,17 +805,6 @@ config SCHED_MC
> making when dealing with multi-core CPU chips at a cost of slightly
> increased overhead in some places. If unsure say N here.
>
> -config IRQ_TIME_ACCOUNTING
> - bool "Fine granularity task level IRQ time accounting"
> - default n
> - ---help---
> - Select this option to enable fine granularity task irq time
> - accounting. This is done by reading a timestamp on each
> - transitions between softirq and hardirq state, so there can be a
> - small performance impact.
> -
> - If in doubt, say N here.
> -
> source "kernel/Kconfig.preempt"
>
> config X86_UP_APIC
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index a62c201..f1b2b63 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -103,14 +103,15 @@ int __init notsc_setup(char *str)
>
> __setup("notsc", notsc_setup);
>
> -static int no_sched_irq_time;
> -
> static int __init tsc_setup(char *str)
> {
> if (!strcmp(str, "reliable"))
> tsc_clocksource_reliable = 1;
> - if (!strncmp(str, "noirqtime", 9))
> - no_sched_irq_time = 1;
> + if (!strncmp(str, "noirqtime", 9)) {
> + printk(KERN_WARNING "tsc: tsc=noirqtime is "
> + "obsolete, use noirqtime instead\n");
> + disable_sched_clock_irqtime();
> + }
> return 1;
> }
>
> @@ -978,8 +979,7 @@ void __init tsc_init(void)
> /* now allow native_sched_clock() to use rdtsc */
> tsc_disabled = 0;
>
> - if (!no_sched_irq_time)
> - enable_sched_clock_irqtime();
> + enable_sched_clock_irqtime();
>
> lpj = ((u64)tsc_khz * 1000);
> do_div(lpj, HZ);
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 7d379a6..9b13f79 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1961,13 +1961,16 @@ extern void sched_clock_idle_wakeup_event(u64 delta_ns);
> #endif
>
> #ifdef CONFIG_IRQ_TIME_ACCOUNTING
> -/*
> - * An i/f to runtime opt-in for irq time accounting based off of sched_clock.
> - * The reason for this explicit opt-in is not to have perf penalty with
> - * slow sched_clocks.
> - */
> -extern void enable_sched_clock_irqtime(void);
> -extern void disable_sched_clock_irqtime(void);
> +extern int sched_clock_irqtime;
> +static inline void enable_sched_clock_irqtime(void)
> +{
> + if (sched_clock_irqtime == -1)
> + sched_clock_irqtime = 1;
> +}
> +static inline void disable_sched_clock_irqtime(void)
> +{
> + sched_clock_irqtime = 0;
> +}
> #else
> static inline void enable_sched_clock_irqtime(void) {}
> static inline void disable_sched_clock_irqtime(void) {}
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 5255c9d..a7ec043 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -757,18 +757,20 @@ static DEFINE_PER_CPU(u64, cpu_hardirq_time);
> static DEFINE_PER_CPU(u64, cpu_softirq_time);
>
> static DEFINE_PER_CPU(u64, irq_start_time);
> -static int sched_clock_irqtime;
>
> -void enable_sched_clock_irqtime(void)
> -{
> - sched_clock_irqtime = 1;
> -}
> +/* -1 if not initialized, 0 if disabled with "noirqtime" kernel option
> + * or after unstable clock was detected, 1 if enabled and active.
> + */
> +int sched_clock_irqtime = -1;
>
> -void disable_sched_clock_irqtime(void)
> +static int __init irqtime_setup(char *str)
> {
> sched_clock_irqtime = 0;
> + return 1;
> }
>
> +__setup("noirqtime", irqtime_setup);
> +
> #ifndef CONFIG_64BIT
> static DEFINE_PER_CPU(seqcount_t, irq_time_seq);
>
> @@ -822,7 +824,7 @@ void account_system_vtime(struct task_struct *curr)
> s64 delta;
> int cpu;
>
> - if (!sched_clock_irqtime)
> + if (sched_clock_irqtime < 1)
> return;
>
> local_irq_save(flags);
> @@ -2853,7 +2855,7 @@ void account_process_tick(struct task_struct *p, int user_tick)
> cputime_t one_jiffy_scaled = cputime_to_scaled(cputime_one_jiffy);
> struct rq *rq = this_rq();
>
> - if (sched_clock_irqtime) {
> + if (sched_clock_irqtime > 0) {
> irqtime_account_process_tick(p, user_tick, rq);
> return;
> }
> @@ -2887,7 +2889,7 @@ void account_steal_ticks(unsigned long ticks)
> void account_idle_ticks(unsigned long ticks)
> {
>
> - if (sched_clock_irqtime) {
> + if (sched_clock_irqtime > 0) {
> irqtime_account_idle_ticks(ticks);
> return;
> }
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 8745ac7..236e814 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -299,6 +299,18 @@ config SCHEDSTATS
> application, you can say N to avoid the very slight overhead
> this adds.
>
> +config IRQ_TIME_ACCOUNTING
> + bool "Fine granularity task level IRQ time accounting"
> + depends on X86 || ARM
> + default n
> + ---help---
> + Select this option to enable fine granularity task irq time
> + accounting. This is done by reading a timestamp on each
> + transitions between softirq and hardirq state, so there can be a
> + small performance impact.
> +
> + If in doubt, say N here.
> +
> config TIMER_STATS
> bool "Collect kernel timers statistics"
> depends on DEBUG_KERNEL && PROC_FS
> --
> 1.7.7.6
>
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