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1e0f42985f
Drop everything except marking the PFN dirty and the relevant tracepoint parts of __handle_changed_spte() when clearing the dirty status of gfns in the TDP MMU. Clearing only the Dirty (or Writable) bit doesn't affect the SPTEs shadow-present status, whether or not the SPTE is a leaf, or change the SPTE's PFN. I.e. other than marking the PFN dirty, none of the functional updates handled by __handle_changed_spte() are relevant. Losing __handle_changed_spte()'s sanity checks does mean that a bug could theoretical go unnoticed, but that scenario is extremely unlikely, e.g. would effectively require a misconfigured or a locking bug elsewhere. Opportunistically remove a comment blurb from __handle_changed_spte() about all modifications to TDP MMU SPTEs needing to invoke said function, that "rule" hasn't been true since fast page fault support was added for the TDP MMU (and perhaps even before). Tested on a VM (160 vCPUs, 160 GB memory) and found that performance of clear dirty log stage improved by ~40% in dirty_log_perf_test (with the full optimization applied). Before optimization: -------------------- Iteration 1 clear dirty log time: 3.638543593s Iteration 2 clear dirty log time: 3.145032742s Iteration 3 clear dirty log time: 3.142340358s Clear dirty log over 3 iterations took 9.925916693s. (Avg 3.308638897s/iteration) After optimization: ------------------- Iteration 1 clear dirty log time: 2.318988110s Iteration 2 clear dirty log time: 1.794470164s Iteration 3 clear dirty log time: 1.791668628s Clear dirty log over 3 iterations took 5.905126902s. (Avg 1.968375634s/iteration) Link: https://lore.kernel.org/all/Y9hXmz%2FnDOr1hQal@google.com Signed-off-by: Vipin Sharma <vipinsh@google.com> Reviewed-by: David Matlack <dmatlack@google.com> [sean: split the switch to atomic-AND to a separate patch] Link: https://lore.kernel.org/r/20230321220021.2119033-7-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 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.