linux-kernel - Re: Abysmal HDD/USB write speed after sleep on a UEFI system

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Date:	Tue, 7 May 2013 15:59:25 +0000 (UTC)
From:	"Artem S. Tashkinov" <t.artem@...os.com>
To:	bhelgaas@...gle.com
Cc:	hancockrwd@...il.com, stern@...land.harvard.edu,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, rjw@...k.pl, psusi@...ntu.com
Subject: Re: Abysmal HDD/USB write speed after sleep on a UEFI system

May 7, 2013 09:25:40 PM, 	Bjorn Helgaas  wrote:
> [+cc Phillip]
>
>> I would suspect that Windows' complaint about the BIOS mucking up the MTRRs
>> is likely the best hint. Likely Windows is detecting the problem and fixing
>> it up on resume, thus it only complains about "reduced resume performance".
>> If the MTRRs are messed up, then quite likely parts of RAM have become
>> uncacheable, causing performance to get randomly slaughtered in various
>> ways.
>>
>> From looking at the code it's not clear if we are checking/restoring the
>> MTRR contents after resume. If not, maybe we should be.
>
>I agree; the MTRR warning is a good hint.  Artem?
>
>Phillip, I cc'd you because you have similar hardware and your
>https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1131468 report is
>slightly similar.  Have you seen anything like this "reduced
>performance after resume" issue?  If so, can you collect /proc/mtrr
>contents before and after suspending?
>

Like Robert Hancock correctly noted the Linux kernel lacks the code to check
for MTTR changes after resume - I'm not a kernel hacker to write such a code ;-)

Likewise there's no code to see if RAM pages have become uncacheable - i.e
I've no idea how to check it either.

According to /proc/mttr nothing changes on resume - only Windows detects
the discrepancy between MTTR regions on resume. dmesg contains no warnings
or errors (aside from usual ACPI SATA warnings - but they happen right on
boot - so I highly doubt the ACPI or SATA layers can be the culprit, since USB
exhibits a similar performance degradation).

In short, there's little to nothing that I can check.

That bug report has nothing to do with my problem - my PC suspends and
resumes more or less correctly - everything works (albeit some parts don't
work as they should). That person also has a very outdated BIOS -  1904 from
08/15/2011. I wouldn't be surprised if BIOS update solved his problem.

Best regards,

Artem
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