linux-kernel - Re: [PATCH 0/2] ata: libahci: devslp fixes

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Date:   Thu, 7 Mar 2019 21:37:30 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Gwendal Grignou <gwendal@...omium.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Tejun Heo <tj@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>, alan.cox@...el.com,
        IDE/ATA development list <linux-ide@...r.kernel.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        rajatja@...omium.org
Subject: Re: [PATCH 0/2] ata: libahci: devslp fixes

Hi,

On 07-03-19 21:27, Gwendal Grignou wrote:
> Srinivas,
> 
> I am looking at problem on a laptop machine that suspends to S01x, but
> link_management is set to max_performance, because the machine is
> connected to a charger.

What is setting it to max_performance when charging?  I assume chrome-os is
running something in userspace to do this (like TLP, but I guess you are not
using TLP) ?

Have you run benchmarks with max_performance vs the default?
I seriously doubt there will be a significant difference, esp.
with a chrome-os style workload.

> Given DVLSP must be set before the laptop suspends ["""One of the
> requirement for modern x86 system to enter lowest power mode  (SLP_S0)
> is SATA IP block to be off."""], the machine never reaches S01x.
> Does it make sense to change the target_lpm_policy at suspend
> (ata_port_suspend()) to min_power and bring it back to the original
> value on resume?

If userspace messes with the setting, then userspace should also
put it back before suspending...

The upstream kernel's default behavior is to have the target level set
to a fixed level independent of the charging state. Could it be this
fixed level is actually max-performance ? If that is the default the
kernel comes up with, that would indicate a kernel bug.

Regards,

Hans



> 
> Gwendal.
> 
> 
> On Mon, Jul 30, 2018 at 10:33 AM Tejun Heo <tj@...nel.org> wrote:
>>
>> On Mon, Jul 30, 2018 at 05:26:45PM +0200, Hans de Goede wrote:
>>> Hi,
>>>
>>> On 30-07-18 17:22, Tejun Heo wrote:
>>>> On Mon, Jul 30, 2018 at 08:15:47AM -0700, Srinivas Pandruvada wrote:
>>>>> Hi Tejan,
>>>>>
>>>>> On Mon, 2018-07-02 at 12:01 -0700, Srinivas Pandruvada wrote:
>>>>>> Some minor fixes to be able to correctly set devslp register
>>>>>> to optimize power.
>>>>>>
>>>>>> Srinivas Pandruvada (2):
>>>>>>    ata: libahci: Correct setting of DEVSLP register
>>>>>>    ata: libahci: Allow reconfigure of DEVSLP register
>>>>>>
>>>>> Are you applying this series?
>>>>
>>>> I was waiting for Hans's reviews.  Hans, what do you think?
>>>
>>> Ah I missed that this was another series. With the caveat that
>>> I do not really know that much about devslp, both patches
>>> seem sensible to me, so both are:
>>>
>>> Reviewed-by: Hans de Goede <hdegoede@...hat.com>
>>
>> Applied 1-2 to libata/for-4.19.
>>
>> Thanks.
>>
>> --
>> tejun
>> --
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