Question: use of FS, GS segment registers in Linux

Hi, What is the use of FS, GS segment registers in kernel and user mode, on x86 and x86-64? Where can I find the related kernel (definition/setup) code? I have read the code in arch/x86/include/asm/segment.h, but still a little confused. Regards, Yuan, Pengfei -- To unsubscribe from this list:

Re: Why not build kernel with -O3

2015-04-08 20:06 GMT+08:00 Austin S Hemmelgarn : > I can't remember any off the top of my head, but it does say explicitly in > the GCC manual to be careful with -O3. IIRC, most of the issues relate to > -O3 enabling -ffast-math (which tends to really mess with code that expects > strict IEEE 754

Re: Why not build kernel with -O3

2015-04-08 20:19 GMT+08:00 Richard Weinberger : > On Wed, Apr 8, 2015 at 3:00 AM, Pengfei Yuan <0xcool...@gmail.com> wrote: >> Could you please provide some examples that I can investigate? >> Thanks! > > It would be awesome if you could find out which gcc optimiz

Re: Why not build kernel with -O3

Could you please provide some examples that I can investigate? Thanks! 2015-04-08 2:05 GMT+08:00 Austin S Hemmelgarn : > On 2015-04-07 06:09, Mike Galbraith wrote: >> On Tue, 2015-04-07 at 15:56 +0800, Pengfei Yuan wrote: >>> I am trying legacy GCC versions. >>> But I a

Re: Why not build kernel with -O3

I am trying legacy GCC versions. But I am not able to try different architectures. 2015-04-07 14:43 GMT+08:00 Mike Galbraith : > On Tue, 2015-04-07 at 11:37 +0800, Pengfei Yuan wrote: >> Hi, >> >> I have conducted some experiments to compare kernels built with -O2 >> an

Why not build kernel with -O3

Hi, I have conducted some experiments to compare kernels built with -O2 and -O3. Here are the results: Application Performance O2 Performance O3 Improvement Apache 127814.14 req/s 130321.24 req/s 1.96% Nginx537589.08 req/s 556723.32 req/s 3.56% MySQL70661.38 tx/s