On Tue, May 7, 2013 at 11:50 AM, Artem S. Tashkinov <t.artem@xxxxxxxxx> wrote: > May 7, 2013 10:27:30 PM, Bjorn Helgaas wrote: > On Tue, May 7, 2013 at 8:59 AM, Artem S. Tashkinov wrote: >>> 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. >> >>I'm not trying to be ungrateful, but maybe you could actually collect >>the info we've asked for and attach it to the bugzilla. It's hard for >>me to get excited about digging into this when all I see is "nothing >>changes in MTRR" and "it's probably not X." I really need some >>concrete data to help rule things out and suggest other things to >>investigate. >> >>Maybe we won't be able to make progress on this until other people >>start hitting similar issues and we can find patterns. > > The pattern is very easy to spot - Linus once told that desktop PCs are > not meant to work properly with suspend. That's kinda strange for me > as I have yet to encounter a PC where Windows fails to work properly > after resume - maybe I'm lucky - who knows. > > Taking into consideration that only few people use Linux, most Linux > users avoid UEFI, very few of them actually use suspend/resume then > it gets very easy to understand why such bug reports are vanishingly > rare. > > Asus themselves could have easily debugged this issue if they were > slightly interested in fixing it, yet their policy is that they only support > Windows, and Linux is not their concern. I can't intuit what the problem is. If you or others can collect data, we can try to fix this. Otherwise, we can't. Bjorn -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
