Re: [Qemu-devel] [PATCH v5 18/19] tcg-arm: Convert to CONFIG_QEMU_LDST_OPTIMIZATION

[Richard Henderson]

On 2013-04-22 13:59, Aurelien Jarno wrote:
> > >+    /* The code buffer is limited to 16MB, with the prologue located
> > >+       at the end of it.  Therefore we needn't care for any out of
> > >+       range branches.  */
> > >+    assert(val - 8 < 0x01fffffd && val - 8 > -0x01fffffd);
> > >+
> > >+    tcg_out_b(s, cond, val);
> While this is currently true, I am not sure we want to get rid of that
> code, and I hope we'll be able to eventually get rid of the 16MB limit.
>
> For me this dramatically reduce the boot time of guests. That said it is
> not a real benchmark, and it should theoretically reduce the
> performances in some cases as doing so interleaves code and data.
> Someone has to spend time doing benchmarks before we can progress on that.

Ok, sure, but how do we progress in the short term?
Certainly rejecting this patch and its changes to tcg_out_goto
is not compatible with approving  19/19, which relies on it.

IMO, tcg_out_goto should be the simple case of goto within a TB,
with only the code for INDEX_goto_tb needing to handle the >16MB case.


r~