Re: [PATCH] get_empty_filp tweaks, inline epoll_init_file()

[Benjamin LaHaise <bcrl@linux.intel.com>]

On Mon, Jan 23, 2006 at 09:44:51PM -0800, Andrew Morton wrote:
> Benjamin LaHaise <bcrl@linux.intel.com> wrote:
> >
> > This patch eliminates a handful of cache references by keeping current 
> >  in a register instead of reloading (helps x86)
> 
> Are you sure it helps?  I was checking that the other day and found that the
> compiler caches current quite competently.

I was looking at the code on x86-64 where it reloads from %gs:0, but x86 
reloads current too.

0xc015599b <get_empty_filp+105>:        mov    $0xfffff000,%eax
0xc01559a0 <get_empty_filp+110>:        and    %esp,%eax
	- eax is current_thread_info()
0xc01559a2 <get_empty_filp+112>:        mov    (%eax),%edx
	- dereference to get current
0xc01559a4 <get_empty_filp+114>:        mov    0x174(%edx),%edx
	- load current->fsuid
0xc01559aa <get_empty_filp+120>:        mov    %edx,0x48(%esi)
	- store in file->f_uid
0xc01559ad <get_empty_filp+123>:        mov    (%eax),%eax
	- reload current
0xc01559af <get_empty_filp+125>:        mov    0x184(%eax),%eax
	- load current->fsgid
0xc01559b5 <get_empty_filp+131>:        mov    %eax,0x4c(%esi)
	- store in file->f_gid

		-ben