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PCIe with lspci

PCIe Width

# lspci -s 81:00.0 -vvv | grep Width
                LnkCap: Port #0, Speed 8GT/s, Width x16, ASPM not supported, Exit Latency L0s unlimited, L1 unlimited
                LnkSta: Speed 8GT/s, Width x16, TrErr- Train- SlotClk+ DLActive- BWMgmt- ABWMgmt-

PCIe Speed

# lspci -s 81:00.0 -vvv | grep Speed
                LnkCap: Port #0, Speed 8GT/s, Width x16, ASPM not supported, Exit Latency L0s unlimited, L1 unlimited
                LnkSta: Speed 8GT/s, Width x16, TrErr- Train- SlotClk+ DLActive- BWMgmt- ABWMgmt-
                LnkCtl2: Target Link Speed: 8GT/s, EnterCompliance- SpeedDis-

# lspci -s 81:00.0 -vvv | grep PCIeGen
                        [V0] Vendor specific: PCIeGen3 x16

PCIe Max Payload Size

# lspci -s 81:00.0 -vvv | grep DevCtl: -C 2
                DevCap: MaxPayload 512 bytes, PhantFunc 0, Latency L0s unlimited, L1 unlimited
                        ExtTag+ AttnBtn- AttnInd- PwrInd- RBE+ FLReset+ SlotPowerLimit 0.000W
                DevCtl: Report errors: Correctable- Non-Fatal+ Fatal+ Unsupported-
                        RlxdOrd- ExtTag- PhantFunc- AuxPwr- NoSnoop- FLReset-
                        MaxPayload 256 bytes, MaxReadReq 4096 bytes

PCIe Max Read Request

# lspci -s 81:00.0 -vvv | grep MaxReadReq
                        MaxPayload 256 bytes, MaxReadReq 1024 bytes

修改PCIe Max Read Request

lspci -s <NIC PCI address> -vvv | grep MaxReadReq
setpci -s <NIC PCI address> 68.w
setpci -s <NIC PCI address> 68.w=3XXX

0 - 128B, 1 - 256B, 2 - 512B, 3 - 1024B, 4 - 2048B and 5 - 4096B.

Maximum PCIe Bandwidth

PCIe 最大带宽计算公式:

Maximum PCIe Bandwidth = SPEED * WIDTH * (1 - ENCODING) - 1Gb/s.

PCIe-Gen3 x8 带宽

Maximum PCIe Bandwidth = 8G * 8 * (1 - 2/130) - 1G = 64G * 0.985 - 1G = ~62Gb/s.

PCIe-Gen2 x16 带宽

Maximum PCIe Bandwidth = 5G * 16 * (1 - 1/5) - 1G = 80G * 0.8 - 1G = ~63Gb/s.