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. Looking into this further, it seems that removing the Thunderbolt controller solves the issue, where XX is the bus after the root port: $ echo 1 | sudo tee /sys/bus/pci/devices/0000\:XX\:00.0/remove Removing the USB controller of the Thunderbolt controller alone can alleviate the problem for a few seconds, before it returns - I have no idea why. Removing the whole Thunderbolt controller from the root solves the problem indefinitely. This is why you cannot reproduce it in QEMU - no Thunderbolt controller. It could be a coincidence that it does it for Thunderbolt, but Mika Westerberg might be interested now. Doing "lspci -n" makes no difference - it suffers the problem whenever the normal command does. Doing "strace lspci -vt" unloaded a lot of information that I cannot summarise. But if you have access to a physical system with Thunderbolt, then you might be able to reproduce the issue and have a better chance of pinpointing the problem than I. Thanks for looking at this. Kind regards, Nicholas
