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e287e43167
Swap the order of the checks in tdp_mmu_iter_cond_resched() so that KVM checks to see if a resched is needed _before_ checking to see if yielding must be disallowed to guarantee forward progress. Iterating over TDP MMU SPTEs is a hot path, e.g. tearing down a root can touch millions of SPTEs, and not needing to reschedule is by far the common case. On the other hand, disallowing yielding because forward progress has not been made is a very rare case. Returning early for the common case (no resched), effectively reduces the number of checks from 2 to 1 for the common case, and should make the code slightly more predictable for the CPU. To resolve a weird conundrum where the forward progress check currently returns false, but the need resched check subtly returns iter->yielded, which _should_ be false (enforced by a WARN), return false unconditionally (which might also help make the sequence more predictable). If KVM has a bug where iter->yielded is left danging, continuing to yield is neither right nor wrong, it was simply an artifact of how the original code was written. Unconditionally returning false when yielding is unnecessary or unwanted will also allow extracting the "should resched" logic to a separate helper in a future patch. Cc: David Matlack <dmatlack@google.com> Reviewed-by: James Houghton <jthoughton@google.com> Link: https://lore.kernel.org/r/20241031170633.1502783-2-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com> |
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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 reStructuredText 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.