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From: Peter Zijlstra <peterz@infradead.org>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-block@vger.kernel.org, cgroups@vger.kernel.org,
	Ingo Molnar <mingo@redhat.com>,
	Andrew Morton <akpm@linuxfoundation.org>,
	Tejun Heo <tj@kernel.org>, Balbir Singh <bsingharora@gmail.com>,
	Mike Galbraith <efault@gmx.de>, Oliver Yang <yangoliver@me.com>,
	Shakeel Butt <shakeelb@google.com>, xxx xxx <x.qendo@gmail.com>,
	Taras Kondratiuk <takondra@cisco.com>,
	Daniel Walker <danielwa@cisco.com>,
	Vinayak Menon <vinmenon@codeaurora.org>,
	Ruslan Ruslichenko <rruslich@cisco.com>,
	kernel-team@fb.com
Subject: Re: [PATCH 6/7] psi: pressure stall information for CPU, memory, and IO
Date: Wed, 9 May 2018 12:46:18 +0200	[thread overview]
Message-ID: <20180509104618.GP12217@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180507210135.1823-7-hannes@cmpxchg.org>

On Mon, May 07, 2018 at 05:01:34PM -0400, Johannes Weiner wrote:

> @@ -2038,6 +2038,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
>  	cpu = select_task_rq(p, p->wake_cpu, SD_BALANCE_WAKE, wake_flags);
>  	if (task_cpu(p) != cpu) {
>  		wake_flags |= WF_MIGRATED;
> +		psi_ttwu_dequeue(p);
>  		set_task_cpu(p, cpu);
>  	}
>  

> +static inline void psi_ttwu_dequeue(struct task_struct *p)
> +{
> +	/*
> +	 * Is the task being migrated during a wakeup? Make sure to
> +	 * deregister its sleep-persistent psi states from the old
> +	 * queue, and let psi_enqueue() know it has to requeue.
> +	 */
> +	if (unlikely(p->in_iowait || (p->flags & PF_MEMSTALL))) {
> +		struct rq_flags rf;
> +		struct rq *rq;
> +		int clear = 0;
> +
> +		if (p->in_iowait)
> +			clear |= TSK_IOWAIT;
> +		if (p->flags & PF_MEMSTALL)
> +			clear |= TSK_MEMSTALL;
> +
> +		rq = __task_rq_lock(p, &rf);
> +		update_rq_clock(rq);
> +		psi_task_change(p, rq_clock(rq), clear, 0);
> +		p->sched_psi_wake_requeue = 1;
> +		__task_rq_unlock(rq, &rf);
> +	}
> +}

Yeah, no... not happening.

We spend a lot of time to never touch the old rq->lock on wakeups. Mason
was the one pushing for that, so he should very well know this.

The one cross-cpu atomic (iowait) is already a problem (the whole iowait
accounting being useless makes it even worse), adding significant remote
prodding is just really bad.

  parent reply	other threads:[~2018-05-09 10:46 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-07 21:01 [PATCH 0/7] " Johannes Weiner
2018-05-07 21:01 ` [PATCH 1/7] mm: workingset: don't drop refault information prematurely Johannes Weiner
2018-05-07 21:01 ` [PATCH 2/7] mm: workingset: tell cache transitions from workingset thrashing Johannes Weiner
2018-05-07 21:01 ` [PATCH 3/7] delayacct: track delays from thrashing cache pages Johannes Weiner
2018-05-07 21:01 ` [PATCH 4/7] sched: loadavg: consolidate LOAD_INT, LOAD_FRAC, CALC_LOAD Johannes Weiner
2018-05-07 21:01 ` [PATCH 5/7] sched: loadavg: make calc_load_n() public Johannes Weiner
2018-05-09  9:49   ` Peter Zijlstra
2018-05-10 13:46     ` Johannes Weiner
2018-05-07 21:01 ` [PATCH 6/7] psi: pressure stall information for CPU, memory, and IO Johannes Weiner
2018-05-08  0:42   ` Randy Dunlap
2018-05-08 14:06     ` Johannes Weiner
2018-05-08  1:35   ` kbuild test robot
2018-05-08  3:04   ` kbuild test robot
2018-05-08 14:05     ` Johannes Weiner
2018-05-09  9:59   ` Peter Zijlstra
2018-05-10 13:49     ` Johannes Weiner
2018-05-09 10:04   ` Peter Zijlstra
2018-05-10 14:10     ` Johannes Weiner
2018-05-09 10:05   ` Peter Zijlstra
2018-05-10 14:13     ` Johannes Weiner
2018-05-09 10:14   ` Peter Zijlstra
2018-05-10 14:18     ` Johannes Weiner
2018-05-09 10:21   ` Peter Zijlstra
2018-05-10 14:24     ` Johannes Weiner
2018-05-09 10:26   ` Peter Zijlstra
2018-05-09 10:46   ` Peter Zijlstra [this message]
2018-05-09 11:38     ` Peter Zijlstra
2018-05-10 13:41       ` Johannes Weiner
2018-05-14  8:33         ` Peter Zijlstra
2018-05-09 10:55   ` Peter Zijlstra
2018-05-09 11:03   ` Vinayak Menon
2018-05-23 13:17     ` Johannes Weiner
2018-05-23 13:19       ` Vinayak Menon
2018-06-07  0:46   ` Suren Baghdasaryan
2018-05-07 21:01 ` [PATCH 7/7] psi: cgroup support Johannes Weiner
2018-05-09 11:07   ` Peter Zijlstra
2018-05-10 14:49     ` Johannes Weiner
2018-05-14 15:39 ` [PATCH 0/7] psi: pressure stall information for CPU, memory, and IO Christopher Lameter
2018-05-14 17:35   ` Bart Van Assche
2018-05-14 18:55   ` Johannes Weiner
2018-05-14 20:15     ` Christopher Lameter
2018-05-26  0:29 ` Suren Baghdasaryan
2018-05-29 18:16   ` Johannes Weiner
2018-05-30 23:32     ` Suren Baghdasaryan

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