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

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Date:	Tue, 30 Apr 2013 22:19:04 -0600
From:	Robert Hancock <hancockrwd@...il.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	"Artem S. Tashkinov" <t.artem@...os.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: Abysmal HDD/USB write speed after sleep on a UEFI system

On 04/29/2013 10:47 PM, Bjorn Helgaas wrote:
> On Sat, Apr 27, 2013 at 4:10 AM, Artem S. Tashkinov <t.artem@...os.com> wrote:
>>>
>>> Did this problem ever get resolved?
>>>
>>
>> Hello,
>>
>> Unfortunately, no. Out of curiosity I've tried booting kernel
>> 3.9-rc8 in EUFI mode but it exhibits the same problem.
>>
>> Right after the boot:
>>
>> [root@...alhost ~]# dd if=/dev/zero of=test bs=64M count=3
>> 3+0 records in
>> 3+0 records out
>> 201326592 bytes (201 MB) copied, 1.08544 s, 185 MB/s
>>
>> After suspend/resume:
>>
>> # dd if=/dev/zero of=test bs=64M count=3
>> 3+0 records in
>> 3+0 records out
>> 201326592 bytes (201 MB) copied, 66.5392 s, 3.0 MB/s
>>
>> That's for my primary SATA-3 HDD.
>>
>> Forgive me my impudence but I believe debugging the USB stack is
>> tangential to this problem. Something far deeper than USB support
>> breaks, but so far no one has come even with the slightest clue of
>> what that might be.
>
> I tend to agree that it sounds like something deeper than USB is
> broken.  I admit I'm just grasping at straws because I don't have any
> good ideas yet.
>
> Here are three easy things you can try:
>
> 1) Collect "lspci -vvv -xxxx" output before and after the
> suspend/resume to investigate the XHCI Unsupported Request errors.
>
> 2) Collect the contents of /proc/mtrr before and after the suspend/resume.
>
> 3) After the suspend/resume, try the "setpci" to set the MSI address
> back to the original value to see if it makes a difference (see my Feb
> 12 message).

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.
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