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From: Peter Zijlstra <peterz@infradead.org>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Wanpeng Li <wanpengli@tencent.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Yauheni Kaliuta <yauheni.kaliuta@redhat.com>,
	Ingo Molnar <mingo@kernel.org>, Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH 04/25] vtime: Spare a seqcount lock/unlock cycle on context switch
Date: Tue, 20 Nov 2018 14:25:12 +0100	[thread overview]
Message-ID: <20181120132512.GQ2131@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <1542163569-20047-5-git-send-email-frederic@kernel.org>

On Wed, Nov 14, 2018 at 03:45:48AM +0100, Frederic Weisbecker wrote:

So I definitely like avoiding that superfluous atomic op, however:

> @@ -730,19 +728,25 @@ static void vtime_account_guest(struct task_struct *tsk,
>  	}
>  }
>  
> +static void __vtime_account_kernel(struct task_struct *tsk,
> +				   struct vtime *vtime)

Your last patch removed a __function, and now you're adding one back :/

>  {
>  	/* We might have scheduled out from guest path */
>  	if (tsk->flags & PF_VCPU)
>  		vtime_account_guest(tsk, vtime);
>  	else
>  		vtime_account_system(tsk, vtime);
> +}
> +
> +void vtime_account_kernel(struct task_struct *tsk)
> +{
> +	struct vtime *vtime = &tsk->vtime;
> +
> +	if (!vtime_delta(vtime))
> +		return;
> +

See here the fast path (is it worth it?)

> +	write_seqcount_begin(&vtime->seqcount);
> +	__vtime_account_kernel(tsk, vtime);
>  	write_seqcount_end(&vtime->seqcount);
>  }

> +void vtime_task_switch_generic(struct task_struct *prev)
>  {
>  	struct vtime *vtime = &prev->vtime;

And observe a distinct lack of that same fast path..

>  
>  	write_seqcount_begin(&vtime->seqcount);
> +	if (is_idle_task(prev))
> +		vtime_account_idle(prev);
> +	else
> +		__vtime_account_kernel(prev, vtime);
>  	vtime->state = VTIME_INACTIVE;
>  	write_seqcount_end(&vtime->seqcount);
>  
> -- 
> 2.7.4
> 

  reply	other threads:[~2018-11-20 13:26 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-14  2:45 [PATCH 00/25] sched/nohz: Make kcpustat vtime aware (Fix kcpustat on nohz_full) Frederic Weisbecker
2018-11-14  2:45 ` [PATCH 01/25] sched/vtime: Fix guest/system mis-accounting on task switch Frederic Weisbecker
2018-11-14  2:45 ` [PATCH 02/25] sched/vtime: Protect idle accounting under vtime seqcount Frederic Weisbecker
2018-11-20 13:19   ` Peter Zijlstra
2018-11-14  2:45 ` [PATCH 03/25] vtime: Rename vtime_account_system() to vtime_account_kernel() Frederic Weisbecker
2018-11-14  2:45 ` [PATCH 04/25] vtime: Spare a seqcount lock/unlock cycle on context switch Frederic Weisbecker
2018-11-20 13:25   ` Peter Zijlstra [this message]
2019-09-25 14:42     ` Frederic Weisbecker
2018-11-14  2:45 ` [PATCH 05/25] sched/vtime: Record CPU under seqcount for kcpustat needs Frederic Weisbecker
2018-11-14  2:45 ` [PATCH 06/25] sched/cputime: Add vtime idle task state Frederic Weisbecker
2018-11-14  2:45 ` [PATCH 07/25] sched/cputime: Add vtime guest " Frederic Weisbecker
2018-11-14  2:45 ` [PATCH 08/25] vtime: Exit vtime before exit_notify() Frederic Weisbecker
2018-11-20 13:54   ` Peter Zijlstra
2018-11-14  2:45 ` [PATCH 09/25] kcpustat: Track running task following vtime sequences Frederic Weisbecker
2018-11-20 13:58   ` Peter Zijlstra
2018-11-14  2:45 ` [PATCH 10/25] context_tracking: Remove context_tracking_active() Frederic Weisbecker
2018-11-14  2:45 ` [PATCH 11/25] context_tracking: s/context_tracking_is_enabled/context_tracking_enabled() Frederic Weisbecker
2018-11-14  2:45 ` [PATCH 12/25] context_tracking: Rename context_tracking_is_cpu_enabled() to context_tracking_enabled_this_cpu() Frederic Weisbecker
2018-11-14  2:45 ` [PATCH 13/25] context_tracking: Introduce context_tracking_enabled_cpu() Frederic Weisbecker
2018-11-20 14:02   ` Peter Zijlstra
2018-11-14  2:45 ` [PATCH 14/25] sched/vtime: Rename vtime_accounting_cpu_enabled() to vtime_accounting_enabled_this_cpu() Frederic Weisbecker
2018-11-14  2:45 ` [PATCH 15/25] sched/vtime: Introduce vtime_accounting_enabled_cpu() Frederic Weisbecker
2018-11-20 14:04   ` Peter Zijlstra
2018-11-14  2:46 ` [PATCH 16/25] sched/cputime: Allow to pass cputime index on user/guest accounting Frederic Weisbecker
2018-11-14  2:46 ` [PATCH 17/25] sched/cputime: Standardize the kcpustat index based accounting functions Frederic Weisbecker
2018-11-14  2:46 ` [PATCH 18/25] vtime: Track nice-ness on top of context switch Frederic Weisbecker
2018-11-20 14:09   ` Peter Zijlstra
2018-11-14  2:46 ` [PATCH 19/25] sched/vite: Handle nice updates under vtime Frederic Weisbecker
2018-11-20 14:17   ` Peter Zijlstra
2018-11-26 15:53     ` Frederic Weisbecker
2018-11-26 16:11       ` Peter Zijlstra
2018-11-26 18:41         ` Frederic Weisbecker
2018-11-14  2:46 ` [PATCH 20/25] sched/kcpustat: Introduce vtime-aware kcpustat accessor Frederic Weisbecker
2018-11-20 14:23   ` Peter Zijlstra
2018-11-20 22:40     ` Frederic Weisbecker
2018-11-21  8:18       ` Peter Zijlstra
2018-11-21  8:35         ` Peter Zijlstra
2018-11-21 16:33         ` Frederic Weisbecker
2018-11-14  2:46 ` [PATCH 21/25] procfs: Use vtime aware " Frederic Weisbecker
2018-11-20 14:24   ` Peter Zijlstra
2018-11-20 22:31     ` Frederic Weisbecker
2018-11-14  2:46 ` [PATCH 22/25] cpufreq: " Frederic Weisbecker
2018-11-14  2:46 ` [PATCH 23/25] leds: Use vtime aware kcpustat accessors Frederic Weisbecker
2018-11-14  2:46 ` [PATCH 24/25] rackmeter: " Frederic Weisbecker
2018-11-14  2:46 ` [PATCH 25/25] sched/vtime: Clarify vtime_task_switch() argument layout Frederic Weisbecker

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