linux-kernel - Re: [PATCH] ACPI: Read TSC upon resume

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <4CBBB3EC.9000609@linux.intel.com>
Date:	Mon, 18 Oct 2010 10:41:48 +0800
From:	Chen Gong <gong.chen@...ux.intel.com>
To:	"Koornstra, Reinoud" <koornstra@...com>
CC:	"Rafael J. Wysocki" <rjw@...k.pl>, Greg KH <gregkh@...e.de>,
	Sameer Nanda <snanda@...omium.org>,
	"lenb@...nel.org" <lenb@...nel.org>,
	"stefan.bader@...onical.com" <stefan.bader@...onical.com>,
	"brad.figg@...onical.com" <brad.figg@...onical.com>,
	"apw@...onical.com" <apw@...onical.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ACPI: Read TSC upon resume

于 10/16/2010 11:03 AM, Koornstra, Reinoud 写道:
>> -----Original Message-----
>> From: linux-acpi-owner@...r.kernel.org [mailto:linux-acpi-
>> owner@...r.kernel.org] On Behalf Of Rafael J. Wysocki
>> Sent: Thursday, October 07, 2010 2:44 PM
>> To: Greg KH
>> Cc: Sameer Nanda; lenb@...nel.org; stefan.bader@...onical.com;
>> brad.figg@...onical.com; apw@...onical.com; linux-acpi@...r.kernel.org;
>> linux-kernel@...r.kernel.org
>> Subject: Re: [PATCH] ACPI: Read TSC upon resume
>>
>> On Thursday, October 07, 2010, Greg KH wrote:
>>> On Thu, Oct 07, 2010 at 11:05:21AM -0700, Sameer Nanda wrote:
>>>> On Thu, Oct 7, 2010 at 10:46 AM, Greg KH<gregkh@...e.de>  wrote:
>>>>> On Thu, Oct 07, 2010 at 10:43:34AM -0700, Sameer Nanda wrote:
>>>>>> On Wed, Oct 6, 2010 at 7:19 PM, Greg KH<gregkh@...e.de>  wrote:
>>>>>>> And are you always going to be printing this out?  Why do we
>> want to
>>>>>>> know this every time?
>>>>>>>
>>>>>>
>>>>>> Yes, every time.  This helps track variance in BIOS resume times
>> within a
>>>>>> single boot.
>>>>>
>>>>> Is that really something that users can do something about?
>>>>
>>>> Aside from complaining to the BIOS vendors, no :)
>>>
>>> Then I would not recommend adding this patch, as it is irrelevant for
>>> 99.9999% of all Linux users.
>>
>> It may be somewhat useful, but the rdtscll() call seems to be x86-
>> specific, in
>> which case it shouldn't be used at this place.
>
> Also, in the case of an intel core 2 duo cpu, the tsc is not stable, hence upon resume the cpu is spinning up and the first tsc's will be slower.
> During idle-time the tsc will not be incremented. The tsc is only stably incremented upon 100% cpu usage. It also doesn't increment faster in turbo mode in case of some core 2 duo and certainly the Nehalem cpu's. Calculating in time in terms of tsc might not be so reliable.
>
If I'm wrong, please feel free to fix me.

I have 2 questions to your answer:

1.  CPU has a flag named constant_tsc to keep TSC always working in a 
constant way, so it is irrelvant to the CPU freq. whether in turbo mode 
or any P-state CPU currently belongs to, TSC should be not affected. 
IIRC, this flag should exist long before, at least before Core 2 duo. If 
so, TSC shoule be stable in this kind of environment.

2. though during idle-time TSC will not be incremented, here I want to
remind it is right before Westmere (TSC not always running), and you 
mentioned "upon resume the cpu is spinning up and the first tsc's will 
be slower", I don't know if this commit cd7240c0b can fix it up.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/