From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH 1/2] x86: suppress event check IPI to
 MWAITing CPUs
Date: Thu, 11 Sep 2014 11:09:51 +0100
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To: Jan Beulich <JBeulich@suse.com>
Cc: Ian Campbell <Ian.Campbell@eu.citrix.com>, xen-devel <xen-devel@lists.xenproject.org>, Keir Fraser <keir@xen.org>, IanJackson <Ian.Jackson@eu.citrix.com>, Tim Deegan <tim@xen.org>
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On 11/09/14 11:07, Jan Beulich wrote:
>>>> On 11.09.14 at 12:02, <andrew.cooper3@citrix.com> wrote:
>> On 11/09/14 10:40, Jan Beulich wrote:
>>> @@ -349,7 +359,7 @@ void mwait_idle_with_hints(unsigned int 
>>>       * Timer deadline passing is the event on which we will be woken via
>>>       * cpuidle_mwait_wakeup. So check it now that the location is armed.
>>>       */
>>> -    if ( expires > NOW() || expires == 0 )
>>> +    if ( (expires > NOW() || expires == 0) && !softirq_pending(cpu) )
>>>      {
>>>          cpumask_set_cpu(cpu, &cpuidle_mwait_flags);
>> Don't you need a smp_wmb() or better here for the results of
>> cpumask_set_cpu() to be guaranteed to be externally visible?  mwait does
>> not appear to be a serialising instruction, and doesn't appear to have
>> any ordering guarantees in the manual.
> I think cpumask_set_cpu() using a LOCKed r-m-w instruction should
> provide all the needed ordering.
>
> Jan
>

Ah yes, and you haven't gotten around to changing the cpumask_*
functions wrt atomicity yet.

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>