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Subject[PATCH] idle using PNI monitor/mwait (take 3)
Date
From
Remade the patch for -mm6. We tested it by removing local_irq_enable()
completely
(and it worked as far as we tested), but I think it would be a cheap
"defensive" code.
Instead of removing it, I moved it to right before __mwait().

Thanks,
Jun
---
diff -ur /build/orig/linux-2.6.0-test4-mm6/arch/i386/kernel/cpu/intel.c
linux-2.6.0-test4-mm6/arch/i386/kernel/cpu/intel.c
--- /build/orig/linux-2.6.0-test4-mm6/arch/i386/kernel/cpu/intel.c
2003-09-05 19:16:26.000000000 -0700
+++ linux-2.6.0-test4-mm6/arch/i386/kernel/cpu/intel.c 2003-09-05
19:22:05.000000000 -0700
@@ -12,6 +12,8 @@

#include "cpu.h"

+extern void select_idle_routine(const struct cpuinfo_x86 *c);
+
#ifdef CONFIG_X86_INTEL_USERCOPY
/*
* Alignment at which movsl is preferred for bulk memory copies.
@@ -163,7 +165,7 @@
}
#endif

-
+ select_idle_routine(c);
if (c->cpuid_level > 1) {
/* supports eax=2 call */
int i, j, n;
diff -ur /build/orig/linux-2.6.0-test4-mm6/arch/i386/kernel/process.c
linux-2.6.0-test4-mm6/arch/i386/kernel/process.c
--- /build/orig/linux-2.6.0-test4-mm6/arch/i386/kernel/process.c
2003-09-05 19:16:26.000000000 -0700
+++ linux-2.6.0-test4-mm6/arch/i386/kernel/process.c 2003-09-05
19:23:01.000000000 -0700
@@ -152,11 +152,56 @@
}
}

+/*
+ * This uses new MONITOR/MWAIT instructions on P4 processors with PNI,
+ * which can obviate IPI to trigger checking of need_resched.
+ * We execute MONITOR against need_resched and enter optimized wait
state
+ * through MWAIT. Whenever someone changes need_resched, we would be
woken
+ * up from MWAIT (without an IPI).
+ */
+static void mwait_idle (void)
+{
+ if (!need_resched()) {
+ set_thread_flag(TIF_POLLING_NRFLAG);
+ do {
+ __monitor((void *)&current_thread_info()->flags,
0, 0);
+ if (need_resched())
+ break;
+
+ local_irq_enable();
+ __mwait(0, 0);
+ } while (!need_resched());
+ clear_thread_flag(TIF_POLLING_NRFLAG);
+ }
+}
+
+void __init select_idle_routine(const struct cpuinfo_x86 *c)
+{
+ if (cpu_has(c, X86_FEATURE_MWAIT)) {
+ printk("Monitor/Mwait feature present.\n");
+ /*
+ * Skip, if setup has overridden idle.
+ * Also, take care of system with asymmetric CPUs.
+ * Use, mwait_idle only if all cpus support it.
+ * If not, we fallback to default_idle()
+ */
+ if (!pm_idle) {
+ pm_idle = mwait_idle;
+ }
+ return;
+ }
+ pm_idle = default_idle;
+ return;
+}
+
static int __init idle_setup (char *str)
{
if (!strncmp(str, "poll", 4)) {
printk("using polling idle threads.\n");
pm_idle = poll_idle;
+ } else if (!strncmp(str, "halt", 4)) {
+ printk("using halt in idle threads.\n");
+ pm_idle = default_idle;
}

return 1;
diff -ur /build/orig/linux-2.6.0-test4-mm6/include/asm-i386/cpufeature.h
linux-2.6.0-test4-mm6/include/asm-i386/cpufeature.h
--- /build/orig/linux-2.6.0-test4-mm6/include/asm-i386/cpufeature.h
2003-08-22 16:58:04.000000000 -0700
+++ linux-2.6.0-test4-mm6/include/asm-i386/cpufeature.h 2003-09-05
19:22:05.000000000 -0700
@@ -71,6 +71,8 @@

/* Intel-defined CPU features, CPUID level 0x00000001 (ecx), word 4 */
#define X86_FEATURE_EST (4*32+ 7) /* Enhanced SpeedStep
*/
+#define X86_FEATURE_MWAIT (4*32+ 3) /* Monitor/Mwait support */
+

/* VIA/Cyrix/Centaur-defined CPU features, CPUID level 0xC0000001, word
5 */
#define X86_FEATURE_XSTORE (5*32+ 2) /* on-CPU RNG present (xstore
insn) */
diff -ur /build/orig/linux-2.6.0-test4-mm6/include/asm-i386/processor.h
linux-2.6.0-test4-mm6/include/asm-i386/processor.h
--- /build/orig/linux-2.6.0-test4-mm6/include/asm-i386/processor.h
2003-09-05 19:17:03.000000000 -0700
+++ linux-2.6.0-test4-mm6/include/asm-i386/processor.h 2003-09-05
19:22:05.000000000 -0700
@@ -272,6 +272,22 @@
#define pc98 0
#endif

+static __inline__ void __monitor(const void *eax, unsigned long ecx,
+ unsigned long edx)
+{
+ /* "monitor %eax,%ecx,%edx;" */
+ asm volatile(
+ ".byte 0x0f,0x01,0xc8;"
+ : :"a" (eax), "c" (ecx), "d"(edx));
+}
+
+static __inline__ void __mwait(unsigned long eax, unsigned long ecx)
+{
+ /* "mwait %eax,%ecx;" */
+ asm volatile(
+ ".byte 0x0f,0x01,0xc9;"
+ : :"a" (eax), "c" (ecx));
+}

/* from system description table in BIOS. Mostly for MCA use, but
others may find it useful. */





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