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Linux 4.14 Has Been Released (kernelnewbies.org)
diegocg quotes Kernel Newbies: Linux 4.11 has been released. This release adds support for bigger memory limits in x86 hardware (128PiB of virtual address space, 4PiB of physical address space); support for AMD Secure Memory Encryption; a new unwinder that provides better kernel traces and a smaller kernel size; support for the zstd compression algorithm has been added to Btrfs and Squashfs; support for zero-copy of data from user memory to sockets; support for Heterogeneous Memory Management that will be needed in future GPUs; better cpufreq behaviour in some corner cases; faster TBL flushing by using the PCID instruction; asynchronous non-blocking buffered reads; and many new drivers and other improvements.
Phoronix has more on the changes in Linux 4.14 -- and notes that its codename is still "Fearless Coyote."
Phoronix has more on the changes in Linux 4.14 -- and notes that its codename is still "Fearless Coyote."
... and PCID is not an instruction. The feature means that there is a "process ID" tag on each entry in the TLB to avoid having to flush them unnecessarily.
The intended benefit is that all entries would not necessarily have to be reloaded from page tables in RAM (or cache) whenever there is a context switch.
"Tagged TLB"s have been available on other CPU architectures for decades -- and have been used by the Linux kernels for those architectures. The feature is pretty recent on Intel x86 CPUs though.
Correct me if I'm mistaken but I think AMD's x86 CPUs do not have PCID specifically but has support for "virtual machine ID" tags on the hypervisor's second-level TLB.
"We mustn't be caught by surprise by our own advancing technology" -- Aldous Huxley
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