Re: [Qemu-devel] commit b1bbfe72 causes huge slowdown with no kvm

[Paolo Bonzini]

Il 20/11/2013 00:00, Luigi Rizzo ha scritto:
> I recently found out that without kvm enabled, and especially
> with -smp 2 or greater, qemu becomes incredibly slow
> (to the point that you can see kernel messages in the
> quest print one character at a time).
> 
> This happens with a Linux host (even with -smp 1)
> and with FreeBSD host (in this case -smp 2 or greater;
> -smp 1 seems to work fine there).


I could not reproduce it; the profile here seems normal, too:

 24,69%  perf-3281.map                       [.] 0x00007f4ab5ac9903
 14,18%  qemu-system-x86_64                  [.] cpu_x86_exec
  2,67%  libglib-2.0.so.0.3800.1             [.] g_source_iter_next
  2,63%  qemu-system-x86_64                  [.] tcg_optimize
  2,47%  qemu-system-x86_64                  [.] helper_pcmpeqb_xmm
  2,28%  qemu-system-x86_64                  [.] phys_page_find
  1,92%  qemu-system-x86_64                  [.] 
address_space_translate_internal
  1,53%  qemu-system-x86_64                  [.] tcg_liveness_analysis
  1,40%  qemu-system-x86_64                  [.] tcg_reg_alloc_op
  1,17%  qemu-system-x86_64                  [.] helper_psubb_xmm
  0,97%  qemu-system-x86_64                  [.] disas_insn
  0,96%  qemu-system-x86_64                  [.] cpu_x86_handle_mmu_fault
  0,92%  qemu-system-x86_64                  [.] tcg_out_opc
  0,92%  qemu-system-x86_64                  [.] helper_pmovmskb_xmm
  0,91%  qemu-system-x86_64                  [.] tlb_set_page
  0,75%  qemu-system-x86_64                  [.] address_space_translate
  0,74%  qemu-system-x86_64                  [.] ldq_phys
  0,61%  qemu-system-x86_64                  [.] tcg_gen_code
  0,58%  qemu-system-x86_64                  [.] helper_le_ldq_mmu
  0,56%  qemu-system-x86_64                  [.] helper_ctz

This is on Linux, -smp 2, booting a RHEL6.4 guest.

Paolo