Re: [PATCH] fast path for rdhwr emulation for TLS

[Atsushi Nemoto <anemo@mba.ocn.ne.jp>]

On Fri, 08 Sep 2006 18:39:08 +0100, Nigel Stephens <nigel@mips.com> wrote:
> > I asked on GCC bugzilla a few days ago but can not got feedback yet.
> > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28126
> >   
> 
> In spite of the GCC issue, is this patch now at the point where it could
> be applied, or at least queued?

GCC 4.2 does not put RDHWR in delay slot now.  Also, there is a
"hackish fix" to prevent gcc move a RDHWR outside of a conditional
(from Richard Sandiford).

For kernel side, my patch can be still applied to current git tree as
is.

But I'm still looking for better solution (silver bullet?) for
cpu_has_vtag_icache case.

How about something like this (and do not touch tlbex.c)?

	LEAF(handle_ri_rdhwr_vivt)
	.set	push
	.set	noat
	.set	noreorder
	/* check if TLB contains a entry for EPC */
	MFC0	K1, CP0_ENTRYHI
	andi	k1, ASID_MASK
	MFC0	k0, CP0_EPC
	andi	k0, PAGE_MASK << 1
	or	k1, k0
	MTC0	k1, CP0_ENTRYHI
	tlbp
	mfc0	k1, CP0_INDEX
	bltz	k1, handle_ri	/* slow path */
	 nop
	/* fall thru */
	LEAF(handle_ri_rdhwr)

I'm wondering if this could work on CONFIG_MIPS_MT_SMTC case...

---
Atsushi Nemoto