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From: Stewart Smith <stewart@linux.vnet.ibm.com>
To: Preeti U Murthy <preeti@linux.vnet.ibm.com>, mpe@ellerman.id.au
Cc: rafael.j.wysocki@intel.com, linuxppc-dev@lists.ozlabs.org,
	linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org
Subject: Re: [PATCH V2] cpuidle/powernv: Read target_residency value of idle states from DT if available
Date: Thu, 29 Jan 2015 09:24:33 +1100	[thread overview]
Message-ID: <m3oapiwnku.fsf@oc8180480414.ibm.com> (raw)
In-Reply-To: <54C8B0E6.5080406@linux.vnet.ibm.com>

Preeti U Murthy <preeti@linux.vnet.ibm.com> writes:
> On 01/28/2015 02:45 PM, Stewart Smith wrote:
>> Preeti U Murthy <preeti@linux.vnet.ibm.com> writes:
>>> The device tree now exposes the residency values for different idle states. Read
>>> these values instead of calculating residency from the latency values. The values
>>> exposed in the DT are validated for optimal power efficiency. However to maintain
>>> compatibility with the older firmware code which does not expose residency
>>> values, use default values as a fallback mechanism. While at it, handle some
>>> cleanups.
>> 
>> From a "I just merged the patch that exports these values from firmware"
>> point of view, using them and falling back looks good.
>> 
>> (I find the hardcoding of snooze in the driver a bit odd, as is the
>
> Snooze is the only software defined idle state, the rest are platform
> specific. The first idle state is usually associated with some sort of a
> polling operation and each architecture has a variant to this. This is
> why we end up hard-coding this idle state in the driver as far as my
> understanding goes.

At least in the PowerISA 2.07 I could only see that lowering priority
would give priority to other threads in the core, I couldn't find
anything saying that or 31,31,31 would end up saving any power... but I
could be looking in the wrong place too.

Basically, I was wanting to check that it's actually written down and
architected somewhere that this is the case and it isn't something too
P7/P8 specific.


WARNING: multiple messages have this Message-ID (diff)
From: Stewart Smith <stewart@linux.vnet.ibm.com>
To: Preeti U Murthy <preeti@linux.vnet.ibm.com>, mpe@ellerman.id.au
Cc: rafael.j.wysocki@intel.com, linuxppc-dev@lists.ozlabs.org,
	linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org
Subject: Re: [PATCH V2] cpuidle/powernv: Read target_residency value of idle states from DT if available
Date: Thu, 29 Jan 2015 09:24:33 +1100	[thread overview]
Message-ID: <m3oapiwnku.fsf@oc8180480414.ibm.com> (raw)
In-Reply-To: <54C8B0E6.5080406@linux.vnet.ibm.com>

Preeti U Murthy <preeti@linux.vnet.ibm.com> writes:
> On 01/28/2015 02:45 PM, Stewart Smith wrote:
>> Preeti U Murthy <preeti@linux.vnet.ibm.com> writes:
>>> The device tree now exposes the residency values for different idle states. Read
>>> these values instead of calculating residency from the latency values. The values
>>> exposed in the DT are validated for optimal power efficiency. However to maintain
>>> compatibility with the older firmware code which does not expose residency
>>> values, use default values as a fallback mechanism. While at it, handle some
>>> cleanups.
>> 
>> From a "I just merged the patch that exports these values from firmware"
>> point of view, using them and falling back looks good.
>> 
>> (I find the hardcoding of snooze in the driver a bit odd, as is the
>
> Snooze is the only software defined idle state, the rest are platform
> specific. The first idle state is usually associated with some sort of a
> polling operation and each architecture has a variant to this. This is
> why we end up hard-coding this idle state in the driver as far as my
> understanding goes.

At least in the PowerISA 2.07 I could only see that lowering priority
would give priority to other threads in the core, I couldn't find
anything saying that or 31,31,31 would end up saving any power... but I
could be looking in the wrong place too.

Basically, I was wanting to check that it's actually written down and
architected somewhere that this is the case and it isn't something too
P7/P8 specific.

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Linuxppc-dev@lists.ozlabs.org
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  reply	other threads:[~2015-01-29  3:35 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-28  2:13 [PATCH V2] cpuidle/powernv: Read target_residency value of idle states from DT if available Preeti U Murthy
2015-01-28  2:13 ` Preeti U Murthy
2015-01-28  9:15 ` Stewart Smith
2015-01-28  9:15   ` Stewart Smith
2015-01-28  9:50   ` Preeti U Murthy
2015-01-28  9:50     ` Preeti U Murthy
2015-01-28 22:24     ` Stewart Smith [this message]
2015-01-28 22:24       ` Stewart Smith
2015-01-30  3:56 ` [V2] " Michael Ellerman

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