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

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Message-ID: <d7caed29-9c7a-6324-9da8-6a9a28bda98a@pfupf.net>
Date:   Fri, 21 Oct 2016 14:41:41 +0200
From:   Juergen Gross <lists@...pf.net>
To:     Peter Zijlstra <peterz@...radead.org>,
        Christian Borntraeger <borntraeger@...ibm.com>
Cc:     linux-arch@...r.kernel.org,
        linux-s390 <linux-s390@...r.kernel.org>, kvm@...r.kernel.org,
        xen-devel@...ts.xenproject.org,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        linux-kernel@...r.kernel.org, Nicholas Piggin <npiggin@...il.com>,
        virtualization@...ts.linux-foundation.org,
        Noam Camus <noamc@...hip.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 2/5] stop_machine: yield CPU during stop machine

On 21/10/16 14:05, Peter Zijlstra wrote:
> 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.

Corrected xen-devel mail address.

Juergen

> 
>> 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
>>
> _______________________________________________
> Virtualization mailing list
> Virtualization@...ts.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/virtualization
> 

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