linux-kernel - Re: [RFC][PATCH 12/13] stop

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Message-ID: <20150623163624.GA24874@redhat.com>
Date:	Tue, 23 Jun 2015 18:36:24 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	paulmck@...ux.vnet.ibm.com, tj@...nel.org, mingo@...hat.com,
	linux-kernel@...r.kernel.org, der.herr@...r.at, dave@...olabs.net,
	riel@...hat.com, viro@...IV.linux.org.uk,
	torvalds@...ux-foundation.org
Subject: Re: [RFC][PATCH 12/13] stop_machine: Remove lglock

On 06/23, Peter Zijlstra wrote:
>
>  void synchronize_sched_expedited(void)
>  {

...

> -	while (try_stop_cpus(cma ? cm : cpu_online_mask,
> -			     synchronize_sched_expedited_cpu_stop,
> -			     NULL) == -EAGAIN) {
> -		put_online_cpus();
> -		atomic_long_inc(&rsp->expedited_tryfail);
> -
> -		/* Check to see if someone else did our work for us. */
> -		s = atomic_long_read(&rsp->expedited_done);
> -		if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
> -			/* ensure test happens before caller kfree */
> -			smp_mb__before_atomic(); /* ^^^ */
> -			atomic_long_inc(&rsp->expedited_workdone1);
> -			free_cpumask_var(cm);
> -			return;
> -		}

...

> +	for_each_online_cpu(cpu) {
> +		struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);

...

> +		stop_one_cpu(cpu, synchronize_sched_expedited_cpu_stop, NULL);

I too thought about something like this change ;)

Not sure I read this patch correctly, but it seems that then you can
remove all rsp->expedited_* members/code ?

Oleg.

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