Subject: Re: [PATCH 2/5] stop_machine: yield CPU during stop machine

From: Peter Zijlstra <[email-masked]>
Date: Fri, 21 Oct 2016 14:05:36 +0200

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 <[email-masked]>
> ---
>  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
>