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[Qemu-devel] [Bug 1672383] Re: Slow Windows XP load after commit a9353fe

From: Maskim Bakulin
Subject: [Qemu-devel] [Bug 1672383] Re: Slow Windows XP load after commit a9353fe897ca2687e5b3385ed39e3db3927a90e0
Date: Tue, 28 Nov 2017 10:30:02 -0000

Supposedly fixed by commit 406bc339b0505fcfc2ffcbca1f05a3756e338a65

** Changed in: qemu
       Status: New => Fix Committed

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  Slow Windows XP load after commit

Status in QEMU:
  Fix Committed

Bug description:
  I've recently discovered, that in QEMU 2.8+ my Windows XP loading time
  has significantly worsened. In 2.7 it took 30-40 second to boot, but
  in 2.8 it became 2-2,5 minutes.

  I've used Git bisect, and found out that the change happened after
  commit a9353fe897ca2687e5b3385ed39e3db3927a90e0, which, as far as I
  can tell from the commit message, handled race condition when
  invalidating breakpoint.

  I've set a breakpoint in static void breakpoint_invalidate(CPUState *cpu, 
target_ulong pc), and here's a backtrace:
  #0  cpu_breakpoint_insert (address@hidden, pc=144, 
      address@hidden, address@hidden)
      at /media/sdd2/qemu-work/exec.c:830
  #1  0x00005555558746ac in hw_breakpoint_insert (address@hidden, 
      address@hidden) at /media/sdd2/qemu-work/target-i386/bpt_helper.c:64
  #2  0x00005555558748ed in cpu_x86_update_dr7 (env=0x555556a7be60, 
      new_dr7=<optimised out>)
      at /media/sdd2/qemu-work/target-i386/bpt_helper.c:160
  #3  0x00007fffa17421f6 in code_gen_buffer ()
  #4  0x000055555577fcb4 in cpu_tb_exec (itb=<optimised out>, 
      itb=<optimised out>, cpu=0x7fff8b7763b0)
      at /media/sdd2/qemu-work/cpu-exec.c:164
  It seems that XP sets some breakpoints during it's load, and it leads to 
frequent TB flushes and slow execution.

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