Re: [Qemu-devel] [PATCH v2 2/7] translate-all.c: Introduce TCGContext *tcg_cur_ctx

[Evgeny Voevodin <e.voevodin@samsung.com>]

On 10/24/2012 01:18 AM, Richard Henderson wrote:
> On 2012-10-23 16:21, Evgeny Voevodin wrote:
>> We will use this pointer from functions where we don't have an
>> interface to pass tcg_ctx as a parameter.
> I don't think this is worthwhile.  It'll just make the whole thing slower,
> passing around unnecessary pointers.
>
>
> r~
>

1. I didn't noticed any slow-down of kernel boot process. Maybe it's 
worth to make more
tests with self modifying code but I don't think so, because
2. The most intensive usage of tcg_cur_ctx is in tcg/tcg-op.h functions. 
If we look carefully at
them then we will see that there are only few functions for which single 
excessive dereferencing
of a pointer leads to any significant slow-down. These functions are 
those which make just one
or two operations and exit. And we should keep in mind that there is 
only single dereference of
a pointer since it is stored in the register for further operations.

Of course some slow-down should present but I found it negligible 
(actually I didn't find it at all).
If there are some common tests for TCG generation speed I can try to run 
them and report results.

Also we can specify tcg_cur_ctx as const and in that case I guess that 
dereferencing of tcg_cur_ctx
should not lead to any slow-down.

Also I can drop tcg_cur_ctx and use tcg_ctx.xxx instead as was in the 
first series.

What about the rest patches?

-- 
Kind regards,
Evgeny Voevodin,
Technical Leader,
Mobile Group,
Samsung Moscow Research Center,
e-mail: e.voevodin@samsung.com