linux-kernel - Re: [PATCH 2/5] stop_machine: yield CPU during stop machine

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Message-ID: <20161021120536.GC3142@twins.programming.kicks-ass.net>
Date:   Fri, 21 Oct 2016 14:05:36 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christian Borntraeger <borntraeger@...ibm.com>
Cc:     Nicholas Piggin <npiggin@...il.com>, linux-kernel@...r.kernel.org,
        linux-s390 <linux-s390@...r.kernel.org>,
        linux-arch@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Noam Camus <noamc@...hip.com>,
        virtualization@...ts.linux-foundation.org,
        xen-devel-request@...ts.xenproject.org, kvm@...r.kernel.org
Subject: Re: [PATCH 2/5] stop_machine: yield CPU during stop machine

On Fri, Oct 21, 2016 at 01:58:55PM +0200, Christian Borntraeger wrote:
> stop_machine can take a very long time if the hypervisor does
> overcommitment for guest CPUs. When waiting for "the one", lets
> give up our CPU by using the new cpu_relax_yield.

This seems something that would apply to most other virt stuff. Lets Cc
a few more lists for that.

> Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
> ---
>  kernel/stop_machine.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
> index ec9ab2f..1eb8266 100644
> --- a/kernel/stop_machine.c
> +++ b/kernel/stop_machine.c
> @@ -194,7 +194,7 @@ static int multi_cpu_stop(void *data)
>  	/* Simple state machine */
>  	do {
>  		/* Chill out and ensure we re-read multi_stop_state. */
> -		cpu_relax();
> +		cpu_relax_yield();
>  		if (msdata->state != curstate) {
>  			curstate = msdata->state;
>  			switch (curstate) {
> -- 
> 2.5.5
>