Re: [Qemu-devel] [PATCH 4/4] target/s390x: Re-implement a few EXECUTE target insns directly

[Richard Henderson]

On 05/25/2017 04:12 PM, Aurelien Jarno wrote:
> On 2017-05-24 15:08, Richard Henderson wrote:
> > While the previous patch is required for proper conformance,
> > the vast majority of target insns are MVC and XC for implementing
> > memmove and memset respectively.  The next most common are CLC,
> > TR, and SVC.
> >
> > Implementing these (and a few others for which we already have
> > an implementation) directly is faster than going through full
> > translation to a TB.
> >
> > Signed-off-by: Richard Henderson <address@hidden>
> > ---
> >   target/s390x/mem_helper.c | 66 ++++++++++++++++++++++++++++++++++++-----------
> >   1 file changed, 51 insertions(+), 15 deletions(-)
>
> I have mixed feelings about this patch. On one side it is correct. On
> the other side, I don't know if it really worth it. With the goto_ptr
> optimization, it can be executed quite fast once it has been translated
> once.

The thing is, I can't identify these being reused at all.  The only case for 
which that would even seem to make sense is memcpy/memset that happens to use 
the same size.  But even then doing the hashing to look up the block is more 
than the decoding required to run the helper directly.


r~