Re: [PATCH] ACPI/NVS: Not save NVS region for new machines to accelerate S3

[Lan Tianyu <tianyu.lan@intel.com>]

On 2014年07月21日 13:01, Chen, Gong wrote:
> On Mon, Jul 21, 2014 at 10:14:31AM +0800, Lan Tianyu wrote:
>> Date: Mon, 21 Jul 2014 10:14:31 +0800
>> From: Lan Tianyu <tianyu.lan@intel.com>
>> To: rjw@rjwysocki.net, lenb@kernel.org, linux-acpi@vger.kernel.org,
>>  linux-kernel@vger.kernel.org, gong.chen@linux.intel.com
>> Subject: Re: [PATCH] ACPI/NVS: Not save NVS region for new machines to
>>  accelerate S3
>> User-Agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:14.0) Gecko/20120714
>>  Thunderbird/14.0
>>
>> On 2014年07月18日 16:00, Chen, Gong wrote:
>>> On Fri, Jul 18, 2014 at 01:55:22PM +0800, Lan Tianyu wrote:
>>>> Date:	Fri, 18 Jul 2014 13:55:22 +0800
>>>> From: Lan Tianyu <tianyu.lan@intel.com>
>>>> To: rjw@rjwysocki.net, lenb@kernel.org
>>>> Cc: Lan Tianyu <tianyu.lan@intel.com>, linux-acpi@vger.kernel.org,
>>>>  linux-kernel@vger.kernel.org
>>>> Subject: [PATCH] ACPI/NVS: Not save NVS region for new machines to
>>>>  accelerate S3
>>>> X-Mailer: git-send-email 1.7.9.5
>>>>
>>>> NVS region is saved and restored unconditionally for machines without
>>>> nvs_nosave quirk during S3. Tested some new machines and the operation
>>>> is not necessary. Saving NVS region also affects S2RAM speed. The time of
>>>> NVS saving and restoring depends on the size of NVS region and it consumes
>>>> 7~10ms normally.
>>>>
>>>> This patch is to make machines produced from 2012 to now not saving NVS region
>>>> to accelerate S3.
>>>>
>>> The year 2012 is a mandatory value in the spec?
>>>
>>
>> No, spec indicates that this is only required for S4 and commit 2a6b697
>> added this behavior because this can fix S3 bug on some machines. But
>> this isn't necessary for all machines and waster time for S3. So this
>> patch is to add time base quirk to change default behavior for new machines.
>>
> If so, I don't think a hard-coded valud in the kernel is a good idea.
> Why not providing a quirk via a command line parameter or module parameter.
> 

There is already a kernel command "acpi_sleep=nonvs_s3" to do that. But
this needs to be set by user. Otherwise, saving/restoring NVS region
also breaks system suspend on some machines and we have added 14
nonvs quirks in the acpisleep_dmi_table.

>From the spec side, it's not necessary and the default behavior should
follow spec. For some special machines which need saving/restoring NVS
region to workaround system suspend, it should be dealt with quirk and
do it when necessary. To avoid regressions on the old machines, the
change only applies to new machines. Other side, not saving/restoring
NVS is also helpful to accelerate S3.

-- 
Best regards
Tianyu Lan