linux-kernel - Re: [PATCH v2 04/11] sched: Simplify wake_up

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Date:   Tue, 19 Oct 2021 10:56:48 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Qian Cai <quic_qiancai@...cinc.com>
Cc:     gor@...ux.ibm.com, jpoimboe@...hat.com, jikos@...nel.org,
        mbenes@...e.cz, pmladek@...e.com, mingo@...nel.org,
        linux-kernel@...r.kernel.org, joe.lawrence@...hat.com,
        fweisbec@...il.com, tglx@...utronix.de, hca@...ux.ibm.com,
        svens@...ux.ibm.com, sumanthk@...ux.ibm.com,
        live-patching@...r.kernel.org, paulmck@...nel.org,
        rostedt@...dmis.org, x86@...nel.org
Subject: Re: [PATCH v2 04/11] sched: Simplify wake_up_*idle*()

On Mon, Oct 18, 2021 at 11:47:32PM -0400, Qian Cai wrote:
> Peter, any thoughts? I did confirm that reverting the commit fixed the issue.
> 
> On 10/13/2021 10:32 AM, Qian Cai wrote:
> > 
> > 
> > On 9/29/2021 11:17 AM, Peter Zijlstra wrote:
> >> --- a/kernel/smp.c
> >> +++ b/kernel/smp.c
> >> @@ -1170,14 +1170,14 @@ void wake_up_all_idle_cpus(void)
> >>  {
> >>  	int cpu;
> >>  
> >> -	preempt_disable();
> >> +	cpus_read_lock();
> >>  	for_each_online_cpu(cpu) {
> >> -		if (cpu == smp_processor_id())
> >> +		if (cpu == raw_smp_processor_id())
> >>  			continue;
> >>  
> >>  		wake_up_if_idle(cpu);
> >>  	}
> >> -	preempt_enable();
> >> +	cpus_read_unlock();

Right, so yesterday I thought: YW2KGrvvv/vSA+97@...ez.programming.kicks-ass.net
but today I might have another idea, lemme go prod at this a bit more.