Re: [Qemu-devel] [PATCH v6 01/50] tcg: Merge opcode arguments into TCGOp

[Emilio G. Cota]

On Mon, Oct 16, 2017 at 10:25:20 -0700, Richard Henderson wrote:
> From: Richard Henderson <address@hidden>
> 
> Rather than have a separate buffer of 10*max_ops entries,
> give each opcode 10 entries.  The result is actually a bit
> smaller and should have slightly more cache locality.
> 
> Signed-off-by: Richard Henderson <address@hidden>

Reviewed-by: Emilio G. Cota <address@hidden>

This gives a small yet measurable perf advantage when booting linux:

 Performance counter stats for 'taskset -c 0 
aarch64-softmmu/qemu-system-aarch64 \
        -M virt,gic_version=3 -cpu cortex-a57 -nographic -m 4096 -netdev \
        user,id=unet,hostfwd=tcp::2222-:22 -device 
virtio-net-device,netdev=unet \
        -drive file=jessie-arm64-die-on-boot.qcow2,id=myblock,index=0,if=none \
        -device virtio-blk-device,drive=myblock -kernel \
        aarch64-current-linux-kernel-only.img \
        -append console=ttyAMA0 root=/dev/vda1 -smp 1' (10 runs):

Before:
       7182.556704      task-clock (msec)         #    0.999 CPUs utilized      
      ( +-  0.11% )
            21,710      context-switches          #    0.003 M/sec              
      ( +-  0.12% )
                 1      cpu-migrations            #    0.000 K/sec              
      ( +- 11.11% )
             7,929      page-faults               #    0.001 M/sec              
      ( +-  1.75% )
    30,280,536,799      cycles                    #    4.216 GHz                
      ( +-  0.11% )
   <not supported>      stalled-cycles-frontend  
   <not supported>      stalled-cycles-backend   
    54,481,515,301      instructions              #    1.80  insns per cycle    
      ( +-  0.09% )
     9,655,822,880      branches                  # 1344.343 M/sec              
      ( +-  0.10% )
       170,594,899      branch-misses             #    1.77% of all branches    
      ( +-  0.10% )

       7.190274755 seconds time elapsed                                         
 ( +-  0.11% )


After:
       7086.254881      task-clock (msec)         #    0.999 CPUs utilized      
      ( +-  0.13% )
            21,598      context-switches          #    0.003 M/sec              
      ( +-  0.07% )
                 1      cpu-migrations            #    0.000 K/sec              
    
             8,099      page-faults               #    0.001 M/sec              
      ( +-  0.97% )
    29,856,727,544      cycles                    #    4.213 GHz                
      ( +-  0.12% )
   <not supported>      stalled-cycles-frontend  
   <not supported>      stalled-cycles-backend   
    53,585,205,542      instructions              #    1.79  insns per cycle    
      ( +-  0.10% )
     9,638,601,205      branches                  # 1360.183 M/sec              
      ( +-  0.10% )
       169,785,181      branch-misses             #    1.76% of all branches    
      ( +-  0.08% )

       7.094560954 seconds time elapsed

That is, a 1.33% perf improvement.

                Emilio