Re: [Qemu-devel] [PATCH 0/4] target/arm: Reduce overhead of cpu_get_tb_cpu_state

[Laurent Desnogues]

Hi Richard,

On Thu, Feb 14, 2019 at 5:07 AM Richard Henderson
<address@hidden> wrote:
>
> We've talked about this before, caching state to reduce the
> amount of computation that happens looking up each TB.
>
> I know that Peter has been concerned that we would not be able to
> reliably maintain all of the places that need to be updates to
> keep this up-to-date.
>
> Well, modulo dirty tricks within linux-user, it appears as if
> exception delivery and return, plus after every TB-ending write
> to a system register is sufficient.
>
> There seems to be a noticable improvement, although wall-time
> is harder to come by -- all of my system-level measurements
> include user input, and my user-level measurements seem to be
> too small to matter.

FWIW this patch series made a run of linux-user AArch64 176.gcc 166.i
go from 29.5s down to 24.5s (on an E5-2650 v2).  Though that'd need
more benchmarks, that looks quite good to me.

Thanks,

Laurent

>
> r~
>
>
> Richard Henderson (4):
>   target/arm: Split out recompute_hflags et al
>   target/arm: Rebuild hflags at el changes and MSR writes
>   target/arm: Assert hflags is correct in cpu_get_tb_cpu_state
>   target/arm: Rely on hflags correct in cpu_get_tb_cpu_state
>
>  target/arm/cpu.h           |  22 ++-
>  target/arm/helper.h        |   3 +
>  target/arm/internals.h     |   4 +
>  linux-user/syscall.c       |   1 +
>  target/arm/cpu.c           |   1 +
>  target/arm/helper-a64.c    |   3 +
>  target/arm/helper.c        | 267 ++++++++++++++++++++++---------------
>  target/arm/machine.c       |   1 +
>  target/arm/op_helper.c     |   1 +
>  target/arm/translate-a64.c |   6 +-
>  target/arm/translate.c     |  14 +-
>  11 files changed, 204 insertions(+), 119 deletions(-)
>
> --
> 2.17.1
>
>