Re: [Qemu-devel] [PATCH v2 2/6] target/mips: reimplement SC instruction emulation and use cmpxchg

["Emilio G. Cota" <cota@braap.org>]

On Thu, Feb 22, 2018 at 19:31:39 +0100, Aleksandar Markovic wrote:
> From: Leon Alrae <lean.alrae@imgtec.com>
> 
> Completely rewrite conditional stores handling. Use cmpxchg.
> 
> This eliminates need for separate implementations of SC instruction
> emulation for user and system emulation.
> 
> Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
> Signed-off-by: Miodrag Dinic <miodrag.dinic@mips.com>
> Signed-off-by: Aleksandar Markovic <aleksandar.markovic@mips.com>
> Reviewed-by: Richard Henderson <rth@twiddle.net>

Tested-by: Emilio G. Cota <cota@braap.org>

Got some stats with qht-bench on mipsel-user -- note that I think
you'd get more meaningful numbers with qht-bench than with
atomic_add-bench, since the latter isn't representative of a useful
workload--rather it's a pathological case unless that doesn't
scale at all unless you increase the range quite a bit.

Also, you might want to add perf numbers to the appropriate commit
log, otherwise they'll be absent from the commit history.

Here are some numbers I just gathered for qht-bench, feel
free to include them in this commit's log:

  mipsel-linux-user tests/qht-bench -d 5 -n 1 -u 20 -g 10000
             Host: AMD Opteron(tm) Processor 6376           
                                                            
  120 +-+-+---------+----------+---------+---------#D-+-+   
      |   +         +          +         +       ## +   |   
      | master ***B***                         ##       |   
  100 +MTTCGv2 ###D###                      ###       +-+   
      |                                   ##            |   
      |                                 ##              |   
   80 +-+                            ###              +-+   
      |                            ##                   |   
      |                        # ##                     |   
   60 +-+                     #D#                     +-+   
      |                    ###                          |   
      |                  ##                             |   
   40 +-+             ###                             +-+   
      |            #D#                                  |   
      |          ##                                     |   
   20 +-+      D#                                     +-+   
      |      ##                                         |   
      |   +##       +          +         +          +   |   
    0 +-+-B****B****B**********B********************B-+-+   
          1         16      Threads      48         64      

  png: https://imgur.com/hTwhw70

Thanks for doing this work!

		Emilio