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

[Richard Henderson <rth@twiddle.net>]

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~