Intel Driver Hints at PCIe Throttling Due to Thermal Pressure

Intel's new Linux driver allows limiting PCI Express link speed to prevent overheating. The "bwctrl" feature throttles down the link speed or shuts off lanes under thermal pressure.

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Bijay Laxmi
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Intel Driver Hints at PCIe Throttling Due to Thermal Pressure

Intel Driver Hints at PCIe Throttling Due to Thermal Pressure

A new Linux driver from Intel suggests that the PCI Express bus may reduce its link speed or even shut off some of its lanes due to thermal pressure, potentially limiting data access for GPUs and SSDs. This feature, referred to as "bwctrl," is designed to prevent overheating by throttling down the PCI Express link speed.

Why this matters: As the industry continues to push the boundaries of high-speed interconnects, effective thermal management becomes crucial to prevent performance degradation. This development may have significant implications for the performance and design of future devices, particularly in the server and data center markets.

The latest revision of Intel's PCI Express driver for Linux allows limiting the PCI Express link speed in case of thermal pressure. The driver creates a cooling device for each port that supports changing speeds, enabling the control of PCIe Link Speed.

Intel engineer Ilpo Järvinen explained in the driver notes,"This series adds PCIe bandwidth controller (bwctrl) and associated PCIe cooling driver to the thermal core side for limiting PCIe Link Speed due to thermal reasons. "He further clarified,"PCIe bandwidth controller is a PCI express bus port service driver. A cooling device is created for each port the service driver finds if they support changing speeds. This series only adds support for controlling PCIe Link Speed. Controlling PCIe Link Width might also be useful but AFAIK, there is no mechanism for that untilPCIe 6.0(L0p) so Link Width throttling is not added by this series."

The PCIe 6.0 specification, announced in 2022 with hardware expected to arrive by March 2024, is anticipated to enable link-width control. Intel appears to be eyeing its cooling solution with servers in mind, but the implications may also affect consumer devices, such as PCIe 5 SSDs, which already require dedicated coolers.

The introduction of this bandwidth throttling feature could have significant implications for the performance of PCIe devices under thermal stress. Even properly-cooled GPUs or SSDs may not be able to access as much data as they normally would if the PCI Express link slows down. In extreme scenarios, the drivers could potentially shut down some of the PCIe lanes, turning a PCIe x16 connection into an x8 connection, for example.

As PCIe speeds continue to increase with each new generation,thermal managementbecomes an increasingly critical factor. The need for aggressive cooling in PCIe 6 devices may lead to PCI Express bandwidth throttling and link-width control as an unfortunate but necessary side effect in extreme thermal scenarios. Intel's Linux driver provides a glimpse into the potential future of PCIe thermal management as the industry pushes the boundaries of high-speed interconnects.