This tool was created out of frustration with the set of tools available for rapid determination of a system PCIe state, specifically the physical maximum and actual speed and width of a PCIe port. The lspci tool is great for querying the kernel PCIe tree, but not so great at presenting useful information in a summary format. In fact, to get the useful information, you have to tell it to be quite verbose.

This is important, if you are debugging a performance issue with a particular function, and trying to understand why, in the face of an otherwise well behaved system, performance appears to be suboptimal. We've seen this now sufficiently frequently that I want very much to find out if my subsystem is in fact not operating at the correct speed/width.

I wanted to see pci id, maximum and actual speed, maximum and actual width, the kernel driver in use, and a description of the device according to the driver. So ... here it is.

landman@leela:~/work/development/pcilist$ sudo ./pcilist.pl

PCIid   MaxWidth ActWidth MaxSpeed ActSpeed     driver       description
00:00.0        4        0        5                           Intel Corporation Haswell-E DMI2 (rev 02)
00:01.0        8        0        8      2.5         pcieport Intel Corporation Haswell-E PCI Express Root Port 1 (rev 02) (prog-if 00 [Normal decode])
00:02.0        8        1        8      2.5         pcieport Intel Corporation Haswell-E PCI Express Root Port 2 (rev 02) (prog-if 00 [Normal decode])
00:02.2        8        8        8        8         pcieport Intel Corporation Haswell-E PCI Express Root Port 2 (rev 02) (prog-if 00 [Normal decode])
00:03.0        8        0        8      2.5         pcieport Intel Corporation Haswell-E PCI Express Root Port 3 (rev 02) (prog-if 00 [Normal decode])
00:03.2        8        8        8        5         pcieport Intel Corporation Haswell-E PCI Express Root Port 3 (rev 02) (prog-if 00 [Normal decode])
00:1c.0        1        0        5      2.5         pcieport Intel Corporation Wellsburg PCI Express Root Port #1 (rev d5) (prog-if 00 [Normal decode])
00:1c.4        4        1        5      2.5         pcieport Intel Corporation Wellsburg PCI Express Root Port #5 (rev d5) (prog-if 00 [Normal decode])
02:00.0        1        1      2.5      2.5    snd_hda_intel Creative Labs SB Recon3D (rev 01)
03:00.0        8        8        8        8          mpt3sas LSI Logic / Symbios Logic SAS2308 PCI-Express Fusion-MPT SAS-2 (rev 05)
05:00.0        8        8        5        5            ixgbe Intel Corporation Ethernet Controller 10-Gigabit X540-AT2 (rev 01)
05:00.1        8        8        5        5            ixgbe Intel Corporation Ethernet Controller 10-Gigabit X540-AT2 (rev 01)
07:00.0        1        1      2.5      2.5                  ASPEED Technology, Inc. AST1150 PCI-to-PCI Bridge (rev 03) (prog-if 00 [Normal decode])
80:02.0        8        8        8        8         pcieport Intel Corporation Haswell-E PCI Express Root Port 2 (rev 02) (prog-if 00 [Normal decode])
80:03.0       16       16        8      2.5         pcieport Intel Corporation Haswell-E PCI Express Root Port 3 (rev 02) (prog-if 00 [Normal decode])
82:00.0       16       16        8      2.5           nvidia NVIDIA Corporation GM107 [GeForce GTX 750 Ti] (rev a2) (prog-if 00 [VGA controller])
82:00.1       16       16        8      2.5    snd_hda_intel NVIDIA Corporation Device 0fbc (rev a1)

Notice the width, speed and other differences.