[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH 0/1] Change default CFLAGS to -O3
From: |
Peter Maydell |
Subject: |
Re: [Qemu-devel] [PATCH 0/1] Change default CFLAGS to -O3 |
Date: |
Mon, 9 Jan 2017 10:33:51 +0000 |
On 9 January 2017 at 10:01, Jin Guojie <address@hidden> wrote:
> * in configure, the default optimization level is changed to O3.
> * Tested successfully on following machines:
>
> | Host machine | Host OS | qemu-system | Debian ISO |
> |-----------------------------------------------------|
> | x86 64 | Fedora25 | i386 | i386 |
> | mips 64 le | Fedora25 | i386 | i386 |
>
> Signed-off-by: Jin Guojie <address@hidden>
>
> Jin Guojie (1):
> Change default CFLAGS to -O3
>
> configure | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
...so what are the measured performance improvements from
this change? As I understand it -O3 is where the "trade off
code size for speed" optimisations kick in, so we need
to benchmark to be sure that the increased icache usage
doesn't outweigh any speed gains. -O3 is not guaranteed
to be strictly better than -O2 (which is why for instance
Debian and Gentoo recommend -O2 as their default).
thanks
-- PMM