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[PATCH] MIPS: Don't branch to eret in TLB refill.

To: linux-mips@linux-mips.org, ralf@linux-mips.org
Subject: [PATCH] MIPS: Don't branch to eret in TLB refill.
From: David Daney <ddaney@caviumnetworks.com>
Date: Tue, 12 May 2009 15:45:16 -0700
Cc: David Daney <ddaney@caviumnetworks.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
If the TLB refill handler is too bit and needs to be split, there is
no need to branch around the split if the branch target would be an
eret.  Since the eret returns from the handler, control flow never
passes it.  A branch to an eret is equivalent to the eret itself.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
---
 arch/mips/mm/tlbex.c |   50 +++++++++++++++++++++++++++++++++-----------------
 1 files changed, 33 insertions(+), 17 deletions(-)

diff --git a/arch/mips/mm/tlbex.c b/arch/mips/mm/tlbex.c
index 4dc4f3e..ffa7104 100644
--- a/arch/mips/mm/tlbex.c
+++ b/arch/mips/mm/tlbex.c
@@ -656,6 +656,7 @@ static void __cpuinit build_r4000_tlb_refill_handler(void)
        struct uasm_reloc *r = relocs;
        u32 *f;
        unsigned int final_len;
+       int split_on_eret;
 
        memset(tlb_handler, 0, sizeof(tlb_handler));
        memset(labels, 0, sizeof(labels));
@@ -684,6 +685,13 @@ static void __cpuinit build_r4000_tlb_refill_handler(void)
        build_update_entries(&p, K0, K1);
        build_tlb_write_entry(&p, &l, &r, tlb_random);
        uasm_l_leave(&l, p);
+
+       /*
+        * Check to see if the eret will be the last instruction
+        * before the split.  If it is, there is no need to branch
+        * around the split, as we are returning.
+        */
+       split_on_eret = (p - tlb_handler == 31);
        uasm_i_eret(&p); /* return from trap */
 
 #ifdef CONFIG_64BIT
@@ -723,28 +731,36 @@ static void __cpuinit build_r4000_tlb_refill_handler(void)
                uasm_copy_handler(relocs, labels, tlb_handler, p, f);
                final_len = p - tlb_handler;
        } else {
-               u32 *split = tlb_handler + 30;
-
-               /*
-                * Find the split point.
-                */
-               if (uasm_insn_has_bdelay(relocs, split - 1))
-                       split--;
+               u32 *split;
+               if (split_on_eret) {
+                       split = tlb_handler + 32;
+               } else {
+                       split = tlb_handler + 30;
+
+                       /*
+                        * Find the split point.
+                        */
+                       if (uasm_insn_has_bdelay(relocs, split - 1))
+                               split--;
+               }
 
                /* Copy first part of the handler. */
                uasm_copy_handler(relocs, labels, tlb_handler, split, f);
                f += split - tlb_handler;
 
-               /* Insert branch. */
-               uasm_l_split(&l, final_handler);
-               uasm_il_b(&f, &r, label_split);
-               if (uasm_insn_has_bdelay(relocs, split))
-                       uasm_i_nop(&f);
-               else {
-                       uasm_copy_handler(relocs, labels, split, split + 1, f);
-                       uasm_move_labels(labels, f, f + 1, -1);
-                       f++;
-                       split++;
+               if (!split_on_eret) {
+                       /* Insert branch. */
+                       uasm_l_split(&l, final_handler);
+                       uasm_il_b(&f, &r, label_split);
+                       if (uasm_insn_has_bdelay(relocs, split))
+                               uasm_i_nop(&f);
+                       else {
+                               uasm_copy_handler(relocs, labels,
+                                                 split, split + 1, f);
+                               uasm_move_labels(labels, f, f + 1, -1);
+                               f++;
+                               split++;
+                       }
                }
 
                /* Copy the rest of the handler. */
-- 
1.6.0.6


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