Parallel CPU Microcode Updates Being Restored To Help Large Core Count Servers

Following Spectre/Meltdown, the Linux CPU microcode updating was made serial while now a new patch pending for the Linux kernel would restore the behavior to be parallelized in order to speed-up the process for large core count servers.

Handling parallel CPU microcode updates can make a meaningful difference on today's large core count systems. An Oracle engineer has volleyed a patch from an Intel developer in trying to get the code into the mainline kernel.

The patch explains, "Microcode update was changed to be serialized due to restrictions after Spectre days. Updating serially on a large multi-socket system can be painful since we do this one CPU at a time. Cloud customers have expressed discontent as services disappear for a prolonged time. The restriction is that only one core goes through the update while other cores are quiesced. The update is now done only on the first thread of each core while other
siblings simply wait for this to complete."

Hopefully this change can make it into Linux 5.4.