From owner-cvs-all  Thu Oct 25  0:54:19 2001
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Date: Thu, 25 Oct 2001 17:53:14 +1000 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: John Baldwin <jhb@FreeBSD.org>
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Subject: Re: cvs commit: src/sys/i386/i386 genassym.c machdep.c swtch.s    
     sys_machdep.c vm_machdep.c src/sys/i386/include pcb.h pcb_ext.h       
  proc.h
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On Wed, 24 Oct 2001, John Baldwin wrote:

> jhb         2001/10/24 17:53:44 PDT
>
>   Modified files:
>     sys/i386/i386        genassym.c machdep.c swtch.s
>                          sys_machdep.c vm_machdep.c
>     sys/i386/include     pcb.h pcb_ext.h proc.h
>   Log:
>   Split the per-process Local Descriptor Table out of the PCB and into
>   struct mdproc.
>
>   Submitted by:	Andrew R. Reiter <arr@watson.org>
>   Silence on:	-current

I was waiting for a review, or at least an rationale for this change.

Why?  It seems to mainly pessimize things by adding an indirection
or two.  Not long ago, and still in RELENG_4, it would have saved
indirections, because p->p_md was direct and p->p_addr was indirect,
but now both td->td_pcb and td->td_proc->p_md are indirect.

Similarly for moving whole user area or whole pcb into p_md.  It would
have saved lots of indirections but would now add a few indirections or
a lot of indirections (depending on how well you load &td->td_proc->p_md
into a register; note that gcc can't optimize multiple references to
td->td_proc into a single load because of aliasing problems).

Bruce


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