Re: [PATCH] KVM: Use thread debug register storage instead of kvm specific data

[Avi Kivity <avi@redhat.com>]

On 09/01/2009 09:12 PM, Andrew Theurer wrote:
> Here's a run from branch debugreg with thread debugreg storage +
> conditionally reload dr6:
>
> user  nice  system   irq  softirq guest   idle  iowait
> 5.79  0.00    9.28  0.08     1.00 20.81  58.78    4.26
> total busy: 36.97
>
> Previous run that had avoided calling adjust_vmx_controls twice:
>
> user  nice  system   irq  softirq guest   idle  iowait
> 5.81  0.00    9.48  0.08    1.04  21.32  57.86    4.41
> total busy: 37.73
>
> A relative reduction CPU cycles of 2%
>    

That was an wasy fruit to pick.  To bad it was a regression that we 
introduced.

> new oprofile:
>
>    
>> samples  %        app name                 symbol name
>> 876648   54.1555  kvm-intel.ko             vmx_vcpu_run
>> 37595     2.3225  qemu-system-x86_64       cpu_physical_memory_rw
>> 35623     2.2006  qemu-system-x86_64       phys_page_find_alloc
>> 24874     1.5366  vmlinux-2.6.31-rc5_debugreg_v2.6.31-rc3-3441-g479fa73-autokern1 native_write_msr_safe
>> 17710     1.0940  libc-2.5.so              memcpy
>> 14664     0.9059  kvm.ko                   kvm_arch_vcpu_ioctl_run
>> 14577     0.9005  qemu-system-x86_64       qemu_get_ram_ptr
>> 12528     0.7739  vmlinux-2.6.31-rc5_debugreg_v2.6.31-rc3-3441-g479fa73-autokern1 native_read_msr_safe
>> 10979     0.6782  vmlinux-2.6.31-rc5_debugreg_v2.6.31-rc3-3441-g479fa73-autokern1 copy_user_generic_string
>> 9979      0.6165  qemu-system-x86_64       virtqueue_get_head
>> 9371      0.5789  vmlinux-2.6.31-rc5_debugreg_v2.6.31-rc3-3441-g479fa73-autokern1 schedule
>> 8333      0.5148  qemu-system-x86_64       virtqueue_avail_bytes
>> 7899      0.4880  vmlinux-2.6.31-rc5_debugreg_v2.6.31-rc3-3441-g479fa73-autokern1 fget_light
>> 7289      0.4503  qemu-system-x86_64       main_loop_wait
>> 7217      0.4458  qemu-system-x86_64       lduw_phys
>>      

This is almost entirely host virtio.  I can reduce native_write_msr_safe 
by a bit, but not much.

>> 6821      0.4214  vmlinux-2.6.31-rc5_debugreg_v2.6.31-rc3-3441-g479fa73-autokern1 audit_syscall_exit
>> 6749      0.4169  vmlinux-2.6.31-rc5_debugreg_v2.6.31-rc3-3441-g479fa73-autokern1 do_select
>> 5919      0.3657  vmlinux-2.6.31-rc5_debugreg_v2.6.31-rc3-3441-g479fa73-autokern1 audit_syscall_entry
>> 5466      0.3377  vmlinux-2.6.31-rc5_debugreg_v2.6.31-rc3-3441-g479fa73-autokern1 kfree
>> 4887      0.3019  vmlinux-2.6.31-rc5_debugreg_v2.6.31-rc3-3441-g479fa73-autokern1 fput
>> 4689      0.2897  vmlinux-2.6.31-rc5_debugreg_v2.6.31-rc3-3441-g479fa73-autokern1 __switch_to
>> 4636      0.2864  vmlinux-2.6.31-rc5_debugreg_v2.6.31-rc3-3441-g479fa73-autokern1 mwait_idle
>>      

Still not idle=poll, it may shave off 0.2%.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.