Linux 5.3 was released
Summary: This release includes support for AMD Navi GPUs; support for the umwait x86 instructions that let processes wait for short amounts of time without spinning loops; a 'utilization clamping' mechanism that is used to boost interactivity in the power-asymmetric CPUs used in phones; a new pidfd_open(2) system call that completes the work done to let users deal with the PID reuse problem; 16 millions of new IPv4 addresses in the 0.0.0.0/8 range are made available; support for Zhaoxin x86 CPUs; support Intel Speed Select for easier power selection in Xeon servers; and support for the lightweight hypervisor ACRN, built for embedded IoT devices. As always, there are many other new drivers and improvements.
New 'pidfd' functionality to help service managers to deal with PID reuse problems
To solve the issue of PID reuse in Unix systems, Linux 5.1 added
Additionally, this release adds polling support for pidfds. This allows process managers to know when a (non-parent) process dies in a race-free way. The notification mechanism used follows the same logic that is currently used when the parent of a task is notified of a child's death. With this patchset it is possible to put pidfds in an {e}poll loop and get reliable notifications for process (i.e. thread-group) exit.
Recommended LWN article: New system calls: pidfd_open() and close_range()
Utilization clamping support in the task scheduler
This release adds utilization clamping support to the task scheduler. This is a refinement of the energy aware scheduling framework for power-asymmetric systems (like ARM big.LITTLE) added in Linux 5.0
Recommended LWN article: Scheduler utilization clamping
Support for AMD Navi GPUs
This release adds initial support for the AMD Navi GPUs in the amdgpu driver, these are the new AMD RX5700 GPUs that just recently became available. This released adds support for the core driver, displays (DCN2), GFX and compute (GFX10), System DMA (SDMA 5), Multimedia decode and encode (VCN2) and Power management.
Support for Zhaoxin x86 CPUs
This release adds support for Zhaoxin x86 Processors. Zhaoxin
Support Intel Speed Select for easier power tuning
This release adds support for Intel Speed Select, a feature only supported on specific Xeon servers. It is a power management technology that lets users to configure their servers for throughput and per-core performance settings, allowing the prioritization of performance for certain workloads running on specific cores by sacrificing the performance of other cores.
Power efficient userspace waiting with the umwait x86 instructions
If an application needs to wait very short times they have to have a spinning loop, which consume power and hurt its thread siblings in a core with hyperthreads. This release enables userspace to use three new instructions that will be added to the upcoming Intel "Tremont" chips: umonitor, umwait and tpause; they let a userspace process wait for short amounts of time without spinning loops, thus letting applications to do those short waits spending less power and not impacting the performance of other hypertreads.
Recommended LWN article: Short waits with umwait
A few millions of new IPv4 addresses
This release contains a trivial, but impacting change: The 0.0.0.0/8 IPv4 range will be accepted by Linux (despite not being declared as such in standards) as a valid address range, allowing for 16 million new IPv4 addresses.
The IPv4 address space includes hundreds of millions of addresses reserved for obscure, or obsolete reasons, or for "future use". Instead of leaving these IP addresses unused, a IPv4 Cleanup Project
Add the IoT ACRN supervisor
This release adds support of the ACRN hypervisor. ACRN is a flexible, lightweight reference hypervisor, built with real-time and safety-criticality in mind, optimized to streamline embedded development through an open source platform. It is built for embedded IoT with small footprint and real-time features. More details can be found in https://projectacrn.org/