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[PATCH 08/10] MIPS: MIPS32R2 optimisations for pipeline stalls and code

To: linux-mips@linux-mips.org, ralf@linux-mips.org
Subject: [PATCH 08/10] MIPS: MIPS32R2 optimisations for pipeline stalls and code size.
From: "Steven J. Hill" <sjhill@mips.com>
Date: Sat, 7 Apr 2012 11:48:33 -0500
Cc: "Steven J. Hill" <sjhill@mips.com>
In-reply-to: <1333817315-30091-1-git-send-email-sjhill@mips.com>
References: <1333817315-30091-1-git-send-email-sjhill@mips.com>
Sender: linux-mips-bounce@linux-mips.org
From: "Steven J. Hill" <sjhill@mips.com>

If the CPU type is selected as MIPS32R2, then we can surround
some code with #ifdef's to reduce the binary size. Detect when
to use 'ehb' instruction to avoid pipeline stalls.

Signed-off-by: Steven J. Hill <sjhill@mips.com>
---
 arch/mips/mm/tlbex.c |   33 ++++++++++++++++++++++++++++-----
 1 file changed, 28 insertions(+), 5 deletions(-)

diff --git a/arch/mips/mm/tlbex.c b/arch/mips/mm/tlbex.c
index 4db0d19..87f57ae 100644
--- a/arch/mips/mm/tlbex.c
+++ b/arch/mips/mm/tlbex.c
@@ -74,10 +74,12 @@ static inline int __maybe_unused bcm1250_m3_war(void)
        return BCM1250_M3_WAR;
 }
 
+#ifndef CONFIG_CPU_MIPS32_R2
 static inline int __maybe_unused r10000_llsc_war(void)
 {
        return R10000_LLSC_WAR;
 }
+#endif
 
 static int use_bbit_insns(void)
 {
@@ -340,6 +342,7 @@ static void __cpuinit build_restore_work_registers(u32 **p)
  */
 extern unsigned long pgd_current[];
 
+# ifndef CONFIG_CPU_MIPS32_R2
 /*
  * The R3000 TLB handler is simple.
  */
@@ -379,6 +382,7 @@ static void __cpuinit build_r3000_tlb_refill_handler(void)
 
        dump_handler((u32 *)ebase, 32);
 }
+# endif /* !CONFIG_CPU_MIPS32_R2 */
 #endif /* CONFIG_MIPS_PGD_C0_CONTEXT */
 
 /*
@@ -449,8 +453,23 @@ static void __cpuinit build_tlb_write_entry(u32 **p, 
struct uasm_label **l,
        }
 
        if (cpu_has_mips_r2) {
-               if (cpu_has_mips_r2_exec_hazard)
-                       uasm_i_ehb(p);
+               /*
+                * The architecture spec says an ehb is required here,
+                * but a number of cores do not have the hazard and
+                * using an ehb causes an expensive pipeline stall.
+                */
+               if (cpu_has_mips_r2_exec_hazard) {
+                       switch (current_cpu_type()) {
+                       case CPU_14K:
+                       case CPU_74K:
+                       case CPU_1074K:
+                               break;
+
+                       default:
+                               uasm_i_ehb(p);
+                               break;
+                       }
+               }
                tlbw(p);
                return;
        }
@@ -910,7 +929,7 @@ build_get_pgde32(u32 **p, unsigned int tmp, unsigned int 
ptr)
 #else
        /*
         * smp_processor_id() << 3 is stored in CONTEXT.
-         */
+        */
        uasm_i_mfc0(p, ptr, C0_CONTEXT);
        UASM_i_LA_mostly(p, tmp, pgdc);
        uasm_i_srl(p, ptr, ptr, 23);
@@ -1513,9 +1532,11 @@ iPTE_SW(u32 **p, struct uasm_reloc **r, unsigned int 
pte, unsigned int ptr,
 # endif
                UASM_i_SC(p, pte, 0, ptr);
 
+#ifndef CONFIG_CPU_MIPS32_R2
        if (r10000_llsc_war())
                uasm_il_beqzl(p, r, pte, label_smp_pgtable_change);
        else
+#endif
                uasm_il_beqz(p, r, pte, label_smp_pgtable_change);
 
 # ifdef CONFIG_64BIT_PHYS_ADDR
@@ -1649,7 +1670,7 @@ build_pte_modifiable(u32 **p, struct uasm_reloc **r,
        }
 }
 
-#ifndef CONFIG_MIPS_PGD_C0_CONTEXT
+#if !defined(CONFIG_MIPS_PGD_C0_CONTEXT) && !defined(CONFIG_CPU_MIPS32_R2)
 
 
 /*
@@ -1803,7 +1824,7 @@ static void __cpuinit build_r3000_tlb_modify_handler(void)
 
        dump_handler(handle_tlbm, ARRAY_SIZE(handle_tlbm));
 }
-#endif /* CONFIG_MIPS_PGD_C0_CONTEXT */
+#endif /* !CONFIG_MIPS_PGD_C0_CONTEXT && !CONFIG_CPU_MIPS32_R2 */
 
 /*
  * R4000 style TLB load/store/modify handlers.
@@ -2120,6 +2141,7 @@ void __cpuinit build_tlb_refill_handler(void)
 #endif
 
        switch (current_cpu_type()) {
+#ifndef CONFIG_CPU_MIPS32_R2
        case CPU_R2000:
        case CPU_R3000:
        case CPU_R3000A:
@@ -2149,6 +2171,7 @@ void __cpuinit build_tlb_refill_handler(void)
                panic("No R8000 TLB refill handler yet");
                break;
 
+#endif /* !CONFIG_CPU_MIPS32_R2 */
        default:
                if (!run_once) {
                        scratch_reg = allocate_kscratch();
-- 
1.7.9.6


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