[Qemu-devel] [PATCH][RFC] x86: use globals for CPU registers

[Laurent Desnogues]

Hello,

this patch is a proposal to use globals for the 8 or 16 CPU
registers on i386 and x86_64.

I measured the improvement in the following conditions:

  - Machine:  i7 920
  - Software:  Fedora11 x86_64 gcc 4.4.1
  - Benchmark: SPEC2000 gcc with expr.i input
  - User mode
  - i386 and x86_64 hosts and targets, with and without the patch
    (8 combinations)

The results are:

qemu-i386_on-i386          15.82user 0.05system 0:15.91elapsed
qemu-i386_on-i386-reg      15.40user 0.02system 0:15.43elapsed
qemu-i386_on-x86_64        15.65user 0.05system 0:15.71elapsed
qemu-i386_on-x86_64-reg    15.11user 0.03system 0:15.15elapsed
qemu-x86_64_on-i386        mmap: No such device or address
qemu-x86_64_on-i386-reg    mmap: No such device or address
qemu-x86_64_on-x86_64      18.42user 0.07system 0:18.49elapsed
qemu-x86_64_on-x86_64-reg  13.22user 0.06system 0:13.31elapsed

Given my lack of knowledge of system QEMU, I will leave it to
someone else to measure the speedup.

A previous version of that patch, that only handled i386 target,
was tested by Malc who got speedup running OpenSSL on his G4.  It
was also sent to Fabrice who asked me to send it to the mailing
list.

The usage of globals is controlled by USE_REGS so that reviewers
can quickly test the benefit (or the lack of it).

Comments are welcome (except for the obvious presence of //
which is only temporary).  I need to optimize a few things once
I'm sure the temporaries (cpu_tmp0, ...) are not used outside of
the modified functions.  x86_64 was coded in a hurry and is
perhaps buggy.


Laurent

Signed-off-by: Laurent Desnogues <address@hidden>

i386-reg2.patch
Description: Text Data