RE: [PATCH] x86: set spincount 1 for x86 hybrid platform [PR109812]

["Zhang, Jun" <jun.zhang@intel.com>]

> -----Original Message-----
> From: Jakub Jelinek <jakub@redhat.com>
> Sent: Tuesday, October 10, 2023 3:57 PM
> To: Zhang, Jun <jun.zhang@intel.com>
> Cc: gcc-patches@gcc.gnu.org; ubizjak@gmail.com; Liu, Hongtao
> <hongtao.liu@intel.com>
> Subject: Re: [PATCH] x86: set spincount 1 for x86 hybrid platform [PR109812]
> 
> On Tue, Oct 10, 2023 at 12:59:52PM +0800, Jun Zhang wrote:
> > include/ChangeLog:
> >
> > 	* omphook.h: define RUNOMPHOOK macro.
> 
> ChangeLog formatting.  The description should start with capital letter.  If you add
> a new file, you should just mention : New file. or something similar.
> 
> But much more importantly, we don't do hooks like that in libgomp, it should be
> better a static inline function where the name shows what it is doing (e.g.
> do_adjust_default_spincount), best in some already existing header (e.g. wait.h),

Sorry, I don't know how to place wait.h. This patch is only for x86.
Wait.h is in libgomp/config/linux/.
if I directly place do_adjust_default_spincount in wait.h,
it maybe need #ifdef  __x86_64__, and also need a wait.h in include/
for other os platform.
if I create a new wait.h in libgomp/config/linux/x86/,
It need copy whole wait.h from libgomp/config/linux/, 
also need a wait.h in include/ for other os platform.
Could you help me?

> and best at the end of the if (!parse_spincount ("GOMP_SPINCOUNT",
> &gomp_spin_count_var)) block in env.c.
> >
> > libgomp/ChangeLog:
> >
> > 	* env.c (initialize_env): add RUNOMPHOOK macro.
> > 	* config/linux/x86/omphook.h: define RUNOMPHOOK macro.
> > ---
> >  include/omphook.h                  |  1 +
> >  libgomp/config/linux/x86/omphook.h | 19 +++++++++++++++++++
> >  libgomp/env.c                      |  3 +++
> >  3 files changed, 23 insertions(+)
> >  create mode 100644 include/omphook.h
> >  create mode 100644 libgomp/config/linux/x86/omphook.h
> >
> > diff --git a/include/omphook.h b/include/omphook.h new file mode
> > 100644 index 00000000000..2ebe3ad57e6
> > --- /dev/null
> > +++ b/include/omphook.h
> > @@ -0,0 +1 @@
> > +#define RUNOMPHOOK()
> > diff --git a/libgomp/config/linux/x86/omphook.h
> > b/libgomp/config/linux/x86/omphook.h
> > new file mode 100644
> > index 00000000000..aefb311cc07
> > --- /dev/null
> > +++ b/libgomp/config/linux/x86/omphook.h
> > @@ -0,0 +1,19 @@
> > +#ifdef __x86_64__
> > +#include "cpuid.h"
> > +
> > +/* only for x86 hybrid platform */
> 
> Comments should again start with capital letter and end with dot and 2 spaces
> before */
> 
> > +#define RUNOMPHOOK()  \
> > +  do \
> > +    { \
> > +      unsigned int eax, ebx, ecx, edx; \
> > +      if ((getenv ("GOMP_SPINCOUNT") == NULL) && (wait_policy < 0) \
> 
> Spurious ()s around the subcondition, the first shouldn't be tested when placed
> right, if condition doesn't fit on one line, each subcondition should be on separate
> line.
> 
> > +	  && __get_cpuid_count (7, 0, &eax, &ebx, &ecx, &edx) \
> 
> If we don't have a macro for the CPUID.07H.0H:EDX[15] bit, there should be a
> comment which says what that bit is.
> 
> > +	  && ((edx >> 15) & 1)) \
> > +	gomp_spin_count_var = 1LL; \
> > +      if (gomp_throttled_spin_count_var > gomp_spin_count_var) \
> > +	gomp_throttled_spin_count_var = gomp_spin_count_var; \
> 
> The above 2 lines won't be needed if placed right.
> 
> 	Jakub