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This merge's Nick's big P9 KVM series, original cover letter follows: KVM: PPC: Book3S HV P9: entry/exit optimisations This reduces radix guest full entry/exit latency on POWER9 and POWER10 by 2x. Nested HV guests should see smaller improvements in their L1 entry/exit, but this is also combined with most L0 speedups also applying to nested entry. nginx localhost throughput test in a SMP nested guest is improved about 10% (in a direct guest it doesn't change much because it uses XIVE for IPIs) when L0 and L1 are patched. It does this in several main ways: - Rearrange code to optimise SPR accesses. Mainly, avoid scoreboard stalls. - Test SPR values to avoid mtSPRs where possible. mtSPRs are expensive. - Reduce mftb. mftb is expensive. - Demand fault certain facilities to avoid saving and/or restoring them (at the cost of fault when they are used, but this is mitigated over a number of entries, like the facilities when context switching processes). PM, TM, and EBB so far. - Defer some sequences that are made just in case a guest is interrupted in the middle of a critical section to the case where the guest is scheduled on a different CPU, rather than every time (at the cost of an extra IPI in this case). Namely the tlbsync sequence for radix with GTSE, which is very expensive. - Reduce locking, barriers, atomics related to the vcpus-per-vcore > 1 handling that the P9 path does not require.
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.