linux-kernel - Re: [PATCH 4/8] nohz: Remove idle task special case

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sun, 14 Jun 2015 07:14:34 +0530
From:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Lameter <cl@...ux.com>,
	Ingo Molnar <mingo@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 4/8] nohz: Remove idle task special case

On 06/11/2015 11:06 PM, Frederic Weisbecker wrote:
> This is a leftover from old days to avoid conflicts with dynticks idle
> code. Now full dynticks and idle dynticks are better integrated and
> interact without known issue.

I am sorry but I fail to understand why the check on idle task was there
in the first place in the below code paths. It would help if you could
clarify this in the changelog as well.

> 
> So lets remove it.
> 
> Cc: Christoph Lameter <cl@...ux.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc; John Stultz <john.stultz@...aro.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> ---
>  kernel/time/tick-sched.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index 812f7a3..324482f 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -208,10 +208,8 @@ void __tick_nohz_full_check(void)
>  	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
> 
>  	if (tick_nohz_full_cpu(smp_processor_id())) {
> -		if (ts->tick_stopped && !is_idle_task(current)) {
> -			if (!can_stop_full_tick())

can_stop_full_tick() would have bailed out if the current task was idle,
since it checks for the number of tasks being greater than 1 to restart
the tick. So why was the check is_idle_task() introduced earlier ?

> -				tick_nohz_restart_sched_tick(ts, ktime_get());
> -		}
> +		if (ts->tick_stopped && !can_stop_full_tick())
> +			tick_nohz_restart_sched_tick(ts, ktime_get());
>  	}
>  }
> 
> @@ -710,7 +708,7 @@ static void tick_nohz_full_stop_tick(struct tick_sched *ts)
>  #ifdef CONFIG_NO_HZ_FULL
>  	int cpu = smp_processor_id();
> 
> -	if (!tick_nohz_full_cpu(cpu) || is_idle_task(current))
> +	if (!tick_nohz_full_cpu(cpu))

If the current task was indeed idle, the check on ts->inidle would have
succeeded in tick_irq_exit() and we would not have reached this function
at all, isn't it? So here too I am unable to understand why we had it in
the first place.

Regards
Preeti U Murthy
>  		return;
> 
>  	if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
> 

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/