Re: [Qemu-devel] [PATCH v3] tcg/ppc: Improve unaligned load/store handling on 64-bit backend

[Richard Henderson]

On 07/20/2015 10:19 PM, Benjamin Herrenschmidt wrote:
> Currently, we get to the slow path for any unaligned access in the
> backend, because we effectively preserve the bottom address bits
> below the alignment requirement when comparing with the TLB entry,
> so any non-0 bit there will cause the compare to fail.
> 
> For the same number of instructions, we can instead add the access
> size - 1 to the address and stick to clearing all the bottom bits.
> 
> That means that normal unaligned accesses will not fallback (the HW
> will handle them fine). Only when crossing a page boundary well we
> end up having a mismatch because we'll end up pointing to the next
> page which cannot possibly be in that same TLB entry.
> 
> Signed-off-by: Benjamin Herrenschmidt <address@hidden>
> ---
> 
> v3. Add MO_ALIGN support for front-ends requiring aligned accesses
> v2. This is the correct version of the patch, the one that
> actually works :-)
> 
>  tcg/ppc/tcg-target.c | 41 +++++++++++++++++++++++++++++++----------
>  1 file changed, 31 insertions(+), 10 deletions(-)

Applied to tcg-next.


r~