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Re: [PATCH v2 0/8] target/sparc: Use tcg_gen_lookup_and_goto_ptr


From: Mark Cave-Ayland
Subject: Re: [PATCH v2 0/8] target/sparc: Use tcg_gen_lookup_and_goto_ptr
Date: Thu, 22 Jun 2023 13:26:22 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0

On 21/06/2023 19:05, Richard Henderson wrote:

Changes from v1:
   * Split into teeny weeny pieces.

   * It turns out the sparc_tr_tb_stop hunk of v1 was buggy,
     in that things that are not simple branches use DYNAMIC_PC,
     e.g. the RETT (return from trap) instruction.

     Introduce DYNAMIC_PC_LOOKUP to distinguish the couple of
     places where we have a dynamic pc, but no other change
     of state (conditional branches, JMPL, RETURN).

   * Drop the change for WRFPRS, because it's too infrequent.
     The WRASI change affects memcpy/memset, so that's more important.

Boots Mark's sol8 install cdrom.  :-)

Top of the profile changes from

     41.55%  qemu-system-sparc              [.] cpu_exec_loop
     14.02%  qemu-system-sparc              [.] cpu_tb_exec
      8.74%  qemu-system-sparc              [.] tb_lookup
      2.11%  qemu-system-sparc              [.] tcg_splitwx_to_rw
      1.63%  memfd:tcg-jit (deleted)        [.] 0x0000000000000004

to

     31.59%  qemu-system-sparc              [.] helper_lookup_tb_ptr
     17.79%  qemu-system-sparc              [.] tb_lookup
      5.38%  qemu-system-sparc              [.] compute_all_sub
      2.38%  qemu-system-sparc              [.] helper_compute_psr
      2.36%  qemu-system-sparc              [.] helper_check_align
      1.79%  memfd:tcg-jit (deleted)        [.] 0x000000000063fc8e

This probably indicates that cpu_get_tb_cpu_state could be
improved to not consume so much overhead.

Nice! I've just run this through all of my sun4m/sun4u/sun4v test images and I don't see any regressions with v2. The guests feel noticeably more responsive too :)

Tested-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>

I've skimmed the patches and without looking in too much detail they seem to be okay so I'm happy to give:

Acked-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>

Side note: the niagara tests require the patch at https://lists.gnu.org/archive/html/qemu-devel/2023-05/msg03537.html which still hasn't been merged yet.

Richard Henderson (8):
   target/sparc: Use tcg_gen_lookup_and_goto_ptr in gen_goto_tb
   target/sparc: Fix npc comparison in sparc_tr_insn_start
   target/sparc: Drop inline markers from translate.c
   target/sparc: Introduce DYNAMIC_PC_LOOKUP
   target/sparc: Use DYNAMIC_PC_LOOKUP for conditional branches
   target/sparc: Use DYNAMIC_PC_LOOKUP for JMPL
   target/sparc: Use DYNAMIC_PC_LOOKUP for v9 RETURN
   target/sparc: Use tcg_gen_lookup_and_goto_ptr for v9 WRASI

  target/sparc/translate.c | 410 ++++++++++++++++++++++-----------------
  1 file changed, 233 insertions(+), 177 deletions(-)


ATB,

Mark.




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