Re: Possible PCI Regression Linux 5.3-rc1

[Logan Gunthorpe <logang@deltatee.com>]

On 2019-07-25 7:18 a.m., Nicholas Johnson wrote:
> On Wed, Jul 24, 2019 at 08:38:14AM -0500, Bjorn Helgaas wrote:
>> On Wed, Jul 24, 2019 at 12:54:00PM +0000, Nicholas Johnson wrote:
>>> Hi all,
>>>
>>> I was just rebasing my patches for linux 5.3-rc1 and noticed a possible 
>>> regression that shows on both of my machines. It is also reproducible 
>>> with the unmodified Ubuntu mainline kernel, downloadable at [1].
>>>
>>> Running the lspci command takes 1-3 seconds with 5.3-rc1 (rather than an 
>>> imperceivable amount of time). Booting with pci.dyndbg does not reveal 
>>> why.
>>>
>>> $ uname -r
>>> 5.3.0-050300rc1-generic
>>> $ time lspci -vt 1>/dev/null
>>>
>>> real	0m2.321s
>>> user	0m0.026s
>>> sys	0m0.000s
>>>
>>> If none of you are aware of this or what is causing it, I will submit a 
>>> bug report to Bugzilla.
>>
>> I wasn't aware of this; thanks for reporting it!  I wasn't able to
>> reproduce this in qemu.  Can you play with "strace -r lspci -vt" and
>> the like?  Maybe try "lspci -n" to see if it's related to looking up
>> the names?
> 
> For a second you had me doubting myself - it could have been a Ubuntu 
> thing. But no, I just reproduced it on Arch Linux, and double checked 
> that it was not doing it on 5.2. Also, the problem occurs even without 
> the PCI kernel parameters which I usually pass.

Ok, can you bisect to find the commit that causes this issue?

Thanks,

Logan