Changeset de96d3b in mainline

Timestamp:

2024-01-03T16:54:15Z (12 months ago)

Author:

Jiří Zárevúcky <zarevucky.jiri@…>

Branches:

master, topic/simplify-dev-export

Children:

00e6288, 25e1490

Parents:

7130754

git-author:

Jiří Zárevúcky <zarevucky.jiri@…> (2024-01-01 04:12:52)

git-committer:

Jiří Zárevúcky <zarevucky.jiri@…> (2024-01-03 16:54:15)

Message:

On x86 CPUs supporting it, use write-combining memory mode for framebuffer

With this, kernel printouts are about three times faster in QEMU.

Location:

kernel

Files:

• arch/amd64/include/arch/mm/page.h (modified) (4 diffs)
• arch/amd64/include/arch/mm/pat.h (added)
• arch/amd64/src/amd64.c (modified) (2 diffs)
• arch/ia32/include/arch/mm/page.h (modified) (2 diffs)
• arch/ia32/include/arch/mm/pat.h (added)
• arch/ia32/src/ia32.c (modified) (2 diffs)
• genarch/src/fb/fb.c (modified) (1 diff)
• generic/include/mm/mm.h (modified) (2 diffs)

kernel/arch/amd64/include/arch/mm/page.h

@@ -192 +192 @@
         unsigned int accessed : 1;
         unsigned int dirty : 1;
-        unsigned int unused : 1;
+        unsigned int pat : 1;
         unsigned int global : 1;
         unsigned int soft_valid : 1;  /**< Valid content even if present bit is cleared. */
@@ -211 +211 @@
             p->writeable << PAGE_WRITE_SHIFT |
             (!p->no_execute) << PAGE_EXEC_SHIFT |
-            p->global << PAGE_GLOBAL_SHIFT);
+            p->global << PAGE_GLOBAL_SHIFT |
+            p->page_write_through << PAGE_WRITE_COMBINE_SHIFT);
 }
 
@@ -225 +226 @@
         pte_t *p = &pt[i];
 
-        p->page_cache_disable = !(flags & PAGE_CACHEABLE);
         p->present = !(flags & PAGE_NOT_PRESENT);
         p->uaccessible = (flags & PAGE_USER) != 0;
@@ -232 +232 @@
         p->global = (flags & PAGE_GLOBAL) != 0;
 
+        if (flags & PAGE_WRITE_COMBINE) {
+                /* We have mapped PCD+PWT bits to write-combine mode via PAT MSR. */
+                /* (If PAT is unsupported, it will default to uncached.) */
+                p->page_cache_disable = 1;
+                p->page_write_through = 1;
+        } else {
+                p->page_cache_disable = !(flags & PAGE_CACHEABLE);
+                p->page_write_through = 0;
+        }
+
         /*
          * Ensure that there is at least one bit set even if the present bit is cleared.

kernel/arch/amd64/src/amd64.c

@@ -60 +60 @@
 #include <arch/vreg.h>
 #include <arch/kseg.h>
+#include <arch/mm/pat.h>
 #include <genarch/pic/pic_ops.h>
 
@@ -115 +116 @@
         /* Disable alignment check */
         write_cr0(read_cr0() & ~CR0_AM);
+
+        /* Use PCD+PWT bit combination in PTE to mean write-combining mode. */
+        if (pat_supported())
+                pat_set_mapping(false, true, true, PAT_TYPE_WRITE_COMBINING);
 
         if (config.cpu_active == 1) {

kernel/arch/ia32/include/arch/mm/page.h

@@ -190 +190 @@
             p->writeable << PAGE_WRITE_SHIFT |
             1 << PAGE_EXEC_SHIFT |
-            p->global << PAGE_GLOBAL_SHIFT);
+            p->global << PAGE_GLOBAL_SHIFT |
+            p->page_write_through << PAGE_WRITE_COMBINE_SHIFT);
 }
 
@@ -197 +198 @@
         pte_t *p = &pt[i];
 
-        p->page_cache_disable = !(flags & PAGE_CACHEABLE);
         p->present = !(flags & PAGE_NOT_PRESENT);
         p->uaccessible = (flags & PAGE_USER) != 0;
         p->writeable = (flags & PAGE_WRITE) != 0;
         p->global = (flags & PAGE_GLOBAL) != 0;
+
+        if (flags & PAGE_WRITE_COMBINE) {
+                /* We have mapped PCD+PWT bits to write-combine mode via PAT MSR. */
+                /* (If PAT is unsupported, it will default to uncached.) */
+                p->page_cache_disable = 1;
+                p->page_write_through = 1;
+        } else {
+                p->page_cache_disable = !(flags & PAGE_CACHEABLE);
+                p->page_write_through = 0;
+        }
 
         /*

kernel/arch/ia32/src/ia32.c

@@ -61 +61 @@
 #include <arch/pm.h>
 #include <arch/vreg.h>
+#include <arch/mm/pat.h>
 
 #ifdef CONFIG_SMP
@@ -104 +105 @@
 {
         pm_init();
+
+        /* Use PCD+PWT bit combination in PTE to mean write-combining mode. */
+        if (pat_supported())
+                pat_set_mapping(false, true, true, PAT_TYPE_WRITE_COMBINING);
 
         if (config.cpu_active == 1) {

kernel/genarch/src/fb/fb.c

@@ -633 +633 @@
 
         instance->addr = (uint8_t *) km_map((uintptr_t) props->addr, fbsize,
-            KM_NATURAL_ALIGNMENT, PAGE_WRITE | PAGE_NOT_CACHEABLE);
+            KM_NATURAL_ALIGNMENT, PAGE_WRITE | PAGE_WRITE_COMBINE);
         if (!instance->addr) {
                 LOG("Unable to map framebuffer.");

kernel/generic/include/mm/mm.h

@@ -46 +46 @@
 #define PAGE_EXEC_SHIFT                 5
 #define PAGE_GLOBAL_SHIFT               6
+#define PAGE_WRITE_COMBINE_SHIFT  7
 
 #define PAGE_NOT_CACHEABLE              (0 << PAGE_CACHEABLE_SHIFT)
@@ -62 +63 @@
 #define PAGE_GLOBAL                     (1 << PAGE_GLOBAL_SHIFT)
 
+#define PAGE_WRITE_COMBINE  (1 << PAGE_WRITE_COMBINE_SHIFT)
+
 #endif