linux-kernel - Re: [PATCH] kvm: add halt_poll

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Message-ID: <54D878AF.5050707@redhat.com>
Date:	Mon, 09 Feb 2015 10:06:55 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
CC:	riel@...hat.com, mtosatti@...hat.com, rkrcmar@...hat.com,
	jan.kiszka@...mens.com, dmatlack@...gle.com
Subject: Re: [PATCH] kvm: add halt_poll_ns module parameter



On 09/02/2015 09:22, Xiao Guangrong wrote:
> 
> 
> On 02/06/2015 08:48 PM, Paolo Bonzini wrote:
> 
>>
>> +unsigned int halt_poll_ns = 0;
>> +module_param(halt_poll_ns, uint, S_IRUGO | S_IWUSR);
>> +
> 
> Can we make this parameter be changeable? So that we can tune it
> on the fly.

It is changeable (S_IWUSR).

>>       finish_wait(&vcpu->wq, &wait);
>> +    cur = ktime_get();
> 
> We can move this into the tracepoint to avoid the workload if the
> tracepoint is not enabled.

You have a point.  I didn't do it because I expect that halt_poll_ns
will be always enabled as soon as it auto-tunes, and in that case you'll
always have to do the ktime_get() for autotuning purposes.

> Otherwise looks good to me.
> 
> Reviewed-by: Xiao Guangrong <guangrong.xiao@...ux.intel.com>

Thanks!

Paolo
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