[PATCH gnumach] cpu_number: Look up cpu kernel_id via lookup table

[Damien Zammit]

This speeds up smp slightly by reducing the cpu_number()
complexity to have no branching, just a look up table.
It also addresses the problem that CPU_NUMBER was only using
raw apic_id as an approximation of the kernel_id.
Other improvements were to remove unnecessary checks now that
the lookup table always resolves to a valid value.
---
 i386/i386/apic.c              | 33 ++++++++++++++++++++++-----------
 i386/i386/apic.h              |  2 ++
 i386/i386/cpu_number.c        | 19 +------------------
 i386/i386/cpu_number.h        |  1 +
 i386/i386at/acpi_parse_apic.c |  2 ++
 5 files changed, 28 insertions(+), 29 deletions(-)

diff --git a/i386/i386/apic.c b/i386/i386/apic.c
index c399074d..2bb8e3f1 100644
--- a/i386/i386/apic.c
+++ b/i386/i386/apic.c
@@ -35,6 +35,11 @@
 static ApicLocalUnit dummy_lapic = {0};
 volatile ApicLocalUnit* lapic = &dummy_lapic;
 
+/* This lookup table of [apic_id] -> kernel_id is initially populated with 
zeroes
+ * so every lookup results in master processor until real kernel ids are 
populated.
+ */
+int cpu_id_lut[UINT8_MAX + 1] = {0};
+
 ApicInfo apic_data;
 
 /*
@@ -137,14 +142,7 @@ apic_get_cpu_apic_id(int kernel_id)
 int
 apic_get_cpu_kernel_id(uint16_t apic_id)
 {
-    int i;
-
-    for (i = 0; i < apic_data.ncpus; i++) {
-        if (apic_data.cpu_lapic_list[i] == apic_id)
-            return i;
-    }
-
-    return -1;
+    return cpu_id_lut[apic_id];
 }
 
 /* apic_get_lapic: returns a reference to the common memory address for Local 
APIC. */
@@ -187,9 +185,6 @@ apic_get_num_ioapics(void)
 int
 apic_get_current_cpu(void)
 {
-    if(lapic == NULL)
-        return -1;
-
     return (lapic->apic_id.r >> 24) & 0xff;
 }
 
@@ -222,6 +217,22 @@ int apic_refit_cpulist(void)
     return 0;
 }
 
+/*
+ * apic_generate_cpu_id_lut: Generate lookup table of cpu kernel ids from apic 
ids
+ */
+void apic_generate_cpu_id_lut(void)
+{
+    int i, apic_id;
+
+    for (i = 0; i < apic_data.ncpus; i++) {
+        apic_id = apic_get_cpu_apic_id(i);
+        if (apic_id >= 0)
+            cpu_id_lut[apic_id] = i;
+        else
+            printf("apic_get_cpu_apic_id(%d) failed...\n", i);
+    }
+}
+
 /*
  * apic_print_info: shows the list of Local APIC and IOAPIC.
  * Shows each CPU and IOAPIC, with Its Kernel ID and APIC ID.
diff --git a/i386/i386/apic.h b/i386/i386/apic.h
index 73e32dfe..e870dcf8 100644
--- a/i386/i386/apic.h
+++ b/i386/i386/apic.h
@@ -238,6 +238,7 @@ uint8_t apic_get_num_ioapics(void);
 int apic_get_current_cpu(void);
 void apic_print_info(void);
 int apic_refit_cpulist(void);
+void apic_generate_cpu_id_lut(void);
 void picdisable(void);
 void lapic_eoi(void);
 void ioapic_irq_eoi(int pin);
@@ -250,6 +251,7 @@ void ioapic_configure(void);
 extern int timer_pin;
 extern void intnull(int unit);
 extern volatile ApicLocalUnit* lapic;
+extern int cpu_id_lut[];
 
 #endif
 
diff --git a/i386/i386/cpu_number.c b/i386/i386/cpu_number.c
index 1d2fab3a..ef19e11f 100644
--- a/i386/i386/cpu_number.c
+++ b/i386/i386/cpu_number.c
@@ -25,23 +25,6 @@
 #if NCPUS > 1
 int cpu_number(void)
 {
-       int kernel_id, apic_id;
-
-       if (bspdone == 0)
-               return 0;
-
-       apic_id = apic_get_current_cpu();
-       if (apic_id < 0) {
-               printf("apic_get_current_cpu() failed, assuming BSP\n");
-               apic_id = 0;
-       }
-
-       kernel_id = apic_get_cpu_kernel_id(apic_id);
-       if (kernel_id < 0) {
-               printf("apic_get_cpu_kernel_id() failed, assuming BSP\n");
-               kernel_id = 0;
-       }
-
-       return kernel_id;
+       return cpu_id_lut[apic_get_current_cpu()];
 }
 #endif
diff --git a/i386/i386/cpu_number.h b/i386/i386/cpu_number.h
index a5658471..c00896e8 100644
--- a/i386/i386/cpu_number.h
+++ b/i386/i386/cpu_number.h
@@ -43,6 +43,7 @@
        movl    %cs:lapic, reg          ;\
        movl    %cs:APIC_ID(reg), reg   ;\
        shrl    $24, reg                ;\
+       movl    %cs:CX(cpu_id_lut, reg), reg    ;\
 
 #ifndef __ASSEMBLER__
 #include "kern/cpu_number.h"
diff --git a/i386/i386at/acpi_parse_apic.c b/i386/i386at/acpi_parse_apic.c
index 27e3410d..9cd861ed 100644
--- a/i386/i386at/acpi_parse_apic.c
+++ b/i386/i386at/acpi_parse_apic.c
@@ -483,6 +483,8 @@ acpi_apic_setup(struct acpi_apic *apic)
             return ACPI_FIT_FAILURE;
     }
 
+    apic_generate_cpu_id_lut();
+
     return ACPI_SUCCESS;
 }
 
-- 
2.40.1