[MIPS] FPU affinity for MT ASE.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

10 files changed, 125 insertions, 2 deletions

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index f9be549645ea..87f0b79c6b15 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -1464,6 +1464,11 @@ config MIPS_VPE_LOADER
 
 endchoice
 
+config MIPS_MT_FPAFF
+        bool "Dynamic FPU affinity for FP-intensive threads"
+        depends on MIPS_MT
+        default y
+
 config MIPS_VPE_LOADER_TOM
         bool "Load VPE program into memory hidden from linux"
         depends on MIPS_VPE_LOADER
diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index 8b393df460a2..199a06e873c6 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -185,6 +185,17 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long usp,
         childregs->cp0_status &= ~(ST0_CU2|ST0_CU1);
         clear_tsk_thread_flag(p, TIF_USEDFPU);
 
+#ifdef CONFIG_MIPS_MT_FPAFF
+        /*
+         * FPU affinity support is cleaner if we track the
+         * user-visible CPU affinity from the very beginning.
+         * The generic cpus_allowed mask will already have
+         * been copied from the parent before copy_thread
+         * is invoked.
+         */
+        p->thread.user_cpus_allowed = p->cpus_allowed;
+#endif /* CONFIG_MIPS_MT_FPAFF */
+
         if (clone_flags & CLONE_SETTLS)
                 ti->tp_value = regs->regs[7];
 
diff --git a/arch/mips/kernel/scall32-o32.S b/arch/mips/kernel/scall32-o32.S
index 4e36b87be1ed..a0ac0e5f61ad 100644
--- a/arch/mips/kernel/scall32-o32.S
+++ b/arch/mips/kernel/scall32-o32.S
@@ -569,8 +569,19 @@ einval:	li	v0, -EINVAL
         sys     sys_tkill               2
         sys     sys_sendfile64          5
         sys     sys_futex               6
+#ifdef CONFIG_MIPS_MT_FPAFF
+        /*
+         * For FPU affinity scheduling on MIPS MT processors, we need to
+         * intercept sys_sched_xxxaffinity() calls until we get a proper hook
+         * in kernel/sched.c.  Considered only temporary we only support these
+         * hooks for the 32-bit kernel - there is no MIPS64 MT processor atm.
+         */
+        sys     mipsmt_sys_sched_setaffinity    3
+        sys     mipsmt_sys_sched_getaffinity    3
+#else
         sys     sys_sched_setaffinity   3
         sys     sys_sched_getaffinity   3       /* 4240 */
+#endif /* CONFIG_MIPS_MT_FPAFF */
         sys     sys_io_setup            2
         sys     sys_io_destroy          1
         sys     sys_io_getevents        5
diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
index dcbfd27071f0..bcf1b10e518f 100644
--- a/arch/mips/kernel/setup.c
+++ b/arch/mips/kernel/setup.c
@@ -529,7 +529,10 @@ void __init setup_arch(char **cmdline_p)
 
 int __init fpu_disable(char *s)
 {
-        cpu_data[0].options &= ~MIPS_CPU_FPU;
+        int i;
+
+        for (i = 0; i < NR_CPUS; i++)
+                cpu_data[i].options &= ~MIPS_CPU_FPU;
 
         return 1;
 }
diff --git a/arch/mips/kernel/smp-mt.c b/arch/mips/kernel/smp-mt.c
index 19b8e4b31b79..57770902b9ae 100644
--- a/arch/mips/kernel/smp-mt.c
+++ b/arch/mips/kernel/smp-mt.c
@@ -150,6 +150,11 @@ void plat_smp_setup(void)
         unsigned long val;
         int i, num;
 
+#ifdef CONFIG_MIPS_MT_FPAFF
+        /* If we have an FPU, enroll ourselves in the FPU-full mask */
+        if (cpu_has_fpu)
+                cpu_set(0, mt_fpu_cpumask);
+#endif /* CONFIG_MIPS_MT_FPAFF */
         if (!cpu_has_mipsmt)
                 return;
 
@@ -312,6 +317,12 @@ void prom_smp_finish(void)
 {
         write_c0_compare(read_c0_count() + (8* mips_hpt_frequency/HZ));
 
+#ifdef CONFIG_MIPS_MT_FPAFF
+        /* If we have an FPU, enroll ourselves in the FPU-full mask */
+        if (cpu_has_fpu)
+                cpu_set(smp_processor_id(), mt_fpu_cpumask);
+#endif /* CONFIG_MIPS_MT_FPAFF */
+
         local_irq_enable();
 }
 
diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index 6336fe8008ec..e9902d89dc0a 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -758,6 +758,36 @@ asmlinkage void do_cpu(struct pt_regs *regs)
                                                 &current->thread.fpu.soft);
                         if (sig)
                                 force_sig(sig, current);
+#ifdef CONFIG_MIPS_MT_FPAFF
+                        else {
+                        /*
+                         * MIPS MT processors may have fewer FPU contexts
+                         * than CPU threads. If we've emulated more than
+                         * some threshold number of instructions, force
+                         * migration to a "CPU" that has FP support.
+                         */
+                         if(mt_fpemul_threshold > 0
+                         && ((current->thread.emulated_fp++
+                            > mt_fpemul_threshold))) {
+                          /*
+                           * If there's no FPU present, or if the
+                           * application has already restricted
+                           * the allowed set to exclude any CPUs
+                           * with FPUs, we'll skip the procedure.
+                           */
+                          if (cpus_intersects(current->cpus_allowed,
+                                                mt_fpu_cpumask)) {
+                            cpumask_t tmask;
+
+                            cpus_and(tmask,
+                                        current->thread.user_cpus_allowed,
+                                        mt_fpu_cpumask);
+                            set_cpus_allowed(current, tmask);
+                            current->thread.mflags |= MF_FPUBOUND;
+                          }
+                         }
+                        }
+#endif /* CONFIG_MIPS_MT_FPAFF */
                 }
 
                 return;
diff --git a/include/asm-mips/cpu-features.h b/include/asm-mips/cpu-features.h
index 3f2b6d9ac45e..254e11ed247b 100644
--- a/include/asm-mips/cpu-features.h
+++ b/include/asm-mips/cpu-features.h
@@ -40,7 +40,7 @@
 #define cpu_has_sb1_cache       (cpu_data[0].options & MIPS_CPU_SB1_CACHE)
 #endif
 #ifndef cpu_has_fpu
-#define cpu_has_fpu             (cpu_data[0].options & MIPS_CPU_FPU)
+#define cpu_has_fpu             (current_cpu_data.options & MIPS_CPU_FPU)
 #endif
 #ifndef cpu_has_32fpr
 #define cpu_has_32fpr           (cpu_data[0].options & MIPS_CPU_32FPR)
diff --git a/include/asm-mips/fpu.h b/include/asm-mips/fpu.h
index 9c828b1f8218..b0f50015e252 100644
--- a/include/asm-mips/fpu.h
+++ b/include/asm-mips/fpu.h
@@ -21,6 +21,10 @@
 #include <asm/processor.h>
 #include <asm/current.h>
 
+#ifdef CONFIG_MIPS_MT_FPAFF
+#include <asm/mips_mt.h>
+#endif
+
 struct sigcontext;
 struct sigcontext32;
 
diff --git a/include/asm-mips/processor.h b/include/asm-mips/processor.h
index 786651340de1..0fb75f0762e0 100644
--- a/include/asm-mips/processor.h
+++ b/include/asm-mips/processor.h
@@ -134,6 +134,12 @@ struct thread_struct {
 
         /* Saved fpu/fpu emulator stuff. */
         union mips_fpu_union fpu;
+#ifdef CONFIG_MIPS_MT_FPAFF
+        /* Emulated instruction count */
+        unsigned long emulated_fp;
+        /* Saved per-thread scheduler affinity mask */
+        cpumask_t user_cpus_allowed;
+#endif /* CONFIG_MIPS_MT_FPAFF */
 
         /* Saved state of the DSP ASE, if available. */
         struct mips_dsp_state dsp;
@@ -159,6 +165,12 @@ struct thread_struct {
 #define MF_N32          MF_32BIT_ADDR
 #define MF_N64          0
 
+#ifdef CONFIG_MIPS_MT_FPAFF
+#define FPAFF_INIT 0, INIT_CPUMASK,
+#else
+#define FPAFF_INIT
+#endif /* CONFIG_MIPS_MT_FPAFF */
+
 #define INIT_THREAD  { \
         /* \
          * saved main processor registers \
@@ -174,6 +186,10 @@ struct thread_struct {
          */ \
         INIT_FPU, \
         /* \
+         * fpu affinity state (null if not FPAFF) \
+         */ \
+        FPAFF_INIT \
+        /* \
          * saved dsp/dsp emulator stuff \
          */ \
         INIT_DSP, \
diff --git a/include/asm-mips/system.h b/include/asm-mips/system.h
index 39026690d9e4..261f71d16a07 100644
--- a/include/asm-mips/system.h
+++ b/include/asm-mips/system.h
@@ -155,6 +155,37 @@ extern asmlinkage void *resume(void *last, void *next, void *next_ti);
 
 struct task_struct;
 
+#ifdef CONFIG_MIPS_MT_FPAFF
+
+/*
+ * Handle the scheduler resume end of FPU affinity management.  We do this
+ * inline to try to keep the overhead down. If we have been forced to run on
+ * a "CPU" with an FPU because of a previous high level of FP computation,
+ * but did not actually use the FPU during the most recent time-slice (CU1
+ * isn't set), we undo the restriction on cpus_allowed.
+ *
+ * We're not calling set_cpus_allowed() here, because we have no need to
+ * force prompt migration - we're already switching the current CPU to a
+ * different thread.
+ */
+
+#define switch_to(prev,next,last)                                       \
+do {                                                                    \
+        if (cpu_has_fpu &&                                              \
+            (prev->thread.mflags & MF_FPUBOUND) &&                      \
+             (!(KSTK_STATUS(prev) & ST0_CU1))) {                        \
+                prev->thread.mflags &= ~MF_FPUBOUND;                    \
+                prev->cpus_allowed = prev->thread.user_cpus_allowed;    \
+        }                                                               \
+        if (cpu_has_dsp)                                                \
+                __save_dsp(prev);                                       \
+        next->thread.emulated_fp = 0;                                   \
+        (last) = resume(prev, next, next->thread_info);                 \
+        if (cpu_has_dsp)                                                \
+                __restore_dsp(current);                                 \
+} while(0)
+
+#else
 #define switch_to(prev,next,last)                                       \
 do {                                                                    \
         if (cpu_has_dsp)                                                \
@@ -163,6 +194,7 @@ do {									\
         if (cpu_has_dsp)                                                \
                 __restore_dsp(current);                                 \
 } while(0)
+#endif
 
 /*
  * On SMP systems, when the scheduler does migration-cost autodetection,