On Thu, Jul 25, 2019 at 09:50:48AM -0600, Logan Gunthorpe wrote: > > > 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? I have done a partial bisect and then found the culprit commit by visual inspection. I would have done the full bisect, but I am using highly underpowered i7-7700K so each round requires 20-30 minutes of compiling. Reversing the following commit solves the issue: commit c2bf1fc212f7e6f25ace1af8f0b3ac061ea48ba5 Author: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> PCI: Add missing link delays required by the PCIe spec Mika, care to weigh in (assuming you are back from four weeks leave)? Clearly this creates delays in "lspci -vt" in some Thunderbolt systems, but not all - otherwise you would have caught it. You mentioned Ice Lake in the commit log so perhaps it works fine on Ice Lake. Thanks, Nicholas > > Thanks, > > Logan
