Re: [HACKERS] Do we need the gcc feature "__builtin_expect" to promote the branches prediction?

On 6 June 2017 at 10:44, Hao Lee wrote: > and another things come into my mind, in some scenario, as we know that the > native library is not the most effective way to do that, such as, allocation > a large amount of memories by using "alloc()"... and "memmove()", so on. As >

Re: [HACKERS] Do we need the gcc feature "__builtin_expect" to promote the branches prediction?

and another things come into my mind, in some scenario, as we know that the native library is not the most effective way to do that, such as, allocation a large amount of memories by using "alloc()"... and "memmove()", so on. As the SIMD instruction became the standard in CPU, therefore, we can

Re: [HACKERS] Do we need the gcc feature "__builtin_expect" to promote the branches prediction?

Hi, On 2017-06-02 16:40:56 +0800, Hao Lee wrote: > Hi all, >There is a lot of "if statement" in system, and GCC provides a > feature,"__builtin_expect", which let compilers know which branch is > mostly run. as we known, miss-prediction will lead the performance > lost(because the CPU

Re: [HACKERS] Do we need the gcc feature "__builtin_expect" to promote the branches prediction?

Okay. Thanks On Fri, Jun 2, 2017 at 7:27 PM, Julien Rouhaud wrote: > On 02/06/2017 12:50, Craig Ringer wrote: > > > > > > On 2 Jun. 2017 16:42, "Hao Lee" > > wrote: > > > > Hi all, > >There is a lot of "if

Re: [HACKERS] Do we need the gcc feature "__builtin_expect" to promote the branches prediction?

On 02/06/2017 12:50, Craig Ringer wrote: > > > On 2 Jun. 2017 16:42, "Hao Lee" > wrote: > > Hi all, >There is a lot of "if statement" in system, and GCC provides > a feature,"__builtin_expect", which let compilers know which

Re: [HACKERS] Do we need the gcc feature "__builtin_expect" to promote the branches prediction?

On 2 Jun. 2017 16:42, "Hao Lee" wrote: Hi all, There is a lot of "if statement" in system, and GCC provides a feature,"__builtin_expect", which let compilers know which branch is mostly run. Compilers and CPUs are really good at guessing this. Humans are wrong about

[HACKERS] Do we need the gcc feature "__builtin_expect" to promote the branches prediction?

Hi all, There is a lot of "if statement" in system, and GCC provides a feature,"__builtin_expect", which let compilers know which branch is mostly run. as we known, miss-prediction will lead the performance lost(because the CPU will thrown away some instructions, and re-fetch some new