Re: [Qemu-devel] [RFC v2 0/5] Dynamic TLB sizing

["Alex Bennée" <alex.bennee@linaro.org>]

Emilio G. Cota <cota@braap.org> writes:

> v1: https://lists.gnu.org/archive/html/qemu-devel/2018-10/msg01146.html
>
> Changes since v1:

Hmm I'm seeing some qtest failures, for example:

  $ make check-qtest-alpha V=1
  ...
  QTEST_QEMU_BINARY=alpha-softmmu/qemu-system-alpha QTEST_QEMU_IMG=qemu-img MALLOC_PERTURB_=${MALLOC_PERTURB_:-$(( ${RANDOM:-0} % 255 + 1))} gtester -k --verbose -m=quick test
  s/boot-serial-test tests/qmp-test tests/qmp-cmd-test tests/device-introspect-test tests/cdrom-test tests/machine-none-test tests/qom-test tests/test-hmp
  TEST: tests/boot-serial-test... (pid=31091)
    /alpha/boot-serial/clipper:                                          Broken pipe
  tests/libqtest.c:129: kill_qemu() detected QEMU death from signal 11 (Segmentation fault) (core dumped)
  FAIL
  GTester: last random seed: R02S948c4a5112fd7682934f4d96e1aff38e
  (pid=31099)
  FAIL: tests/boot-serial-test


>
> - Add tlb_index and tlb_entry helpers from Richard
>
> - Introduce sizeof_tlb() and tlb_n_entries()
>
> - Extract tlb_mask as its own array in CPUArchState, as
>   suggested by Richard. For the associated helpers (tlb_index etc)
>   I tried several approaches, and performance-wise they're all
>   the same, so went for the simplest implementation.
>
> - Use uintptr_t for tlb_mask, as done in Richard's patch
>   + tcg/i386: use hrexw when reading tlb_mask
>   + Define tlbtype and tlbrexw solely based on TARGET_PAGE_BITS
>
> - Rename tlb_is_invalid to tlb_entry_is_empty, comparing all
>   fields (except .addend) against -1.
>
> - Rename CPUTLBDesc.used to .n_used_entries.
>
> - Drop the MIN/MAX CPU_TLB_BITS patches, defining instead
>   some values for MIN/MAX as well as a default.
>
> - Use new_size and old_size consistently in the resizing function,
>   as suggested by Richard.
>
> - Add an additional chart to the last patch, where softmmu
>   performance is compared against user-mode:
>     https://imgur.com/a/eXkjMCE
>
> You can fetch this series from:
>   https://github.com/cota/qemu/tree/tlb-dyn-v2
>
> Note that it applies on top of my tlb-lock-v4 series:
>   https://lists.gnu.org/archive/html/qemu-devel/2018-10/msg01421.html
>
> Thanks,
>
> 		Emilio


--
Alex Bennée