RE: [Xen-devel] [PATCH] X86: Prefer TSC-deadline timer in Xen

["Wei, Gang" <gang.wei@xxxxxxxxx>]

Resend after merging Jan's comments.

-Jimmy
---------------------------------------------------
X86: Prefer TSC-deadline timer in Xen

The new TSC Deadline Timer offers system software a low overhead
per-logical-thread deadline timer in TSC units.

The timer is implemented via a new architectural 64-bit register,
IA32_TSC_DEADLINE_MSR. Reads and writes of this MSR occur in program order,
but are non-serializing.

The support for this feature is indicated by
CPUID.01H:ECX.TSC_Deadline[bit 24] = 1 as documented in the Intel Architectures
Software Developer's Manual.

The LOCAL APIC on new processors has a mode where its underlying hardware timer
can now be accessed via the non-serializing IA32_TSC_DEADLINE_MSR in TSC tick
units.

If this mode is present, prefer it over the traditional LAPIC timer mode.
KERN_DEBUG dmesg will print "TSC deadline timer enabled" when TDT is used.

Bootparam "tdt=off" is available to revert to LAPIC timer mode.

This patch is based on original work by Len Brown for Linux kernel.

cc: Len Brown <len.brown@xxxxxxxxx>
Signed-off-by: Wei Gang <gang.wei@xxxxxxxxx>

diff -r 0dc0bc411035 xen/arch/x86/apic.c
--- a/xen/arch/x86/apic.c       Thu Oct 21 18:51:36 2010 +0100
+++ b/xen/arch/x86/apic.c       Sat Oct 30 04:03:03 2010 +0800
@@ -37,6 +37,15 @@
 #include <asm/asm_defns.h> /* for BUILD_SMP_INTERRUPT */
 #include <mach_apic.h>
 #include <io_ports.h>
+
+#define APIC_TIMER_MODE_ONESHOT         (0 << 17)
+#define APIC_TIMER_MODE_PERIODIC        (1 << 17)
+#define APIC_TIMER_MODE_TSC_DEADLINE    (2 << 17)
+#define APIC_TIMER_MODE_MASK            (3 << 17)
+
+static int tdt_enabled __read_mostly;
+static int tdt_enable __read_mostly = 1;
+boolean_param("tdt", tdt_enable);
 
 static struct {
     int active;
@@ -1198,6 +1207,13 @@ static void __setup_APIC_LVTT(unsigned i
     lvtt_value = /*APIC_LVT_TIMER_PERIODIC |*/ LOCAL_TIMER_VECTOR;
     if (!APIC_INTEGRATED(ver))
         lvtt_value |= SET_APIC_TIMER_BASE(APIC_TIMER_BASE_DIV);
+
+    if ( tdt_enabled )
+    {
+        lvtt_value &= (~APIC_TIMER_MODE_MASK);
+        lvtt_value |= APIC_TIMER_MODE_TSC_DEADLINE;
+    }
+
     apic_write_around(APIC_LVTT, lvtt_value);
 
     tmp_value = apic_read(APIC_TDCR);
@@ -1311,6 +1327,12 @@ void __init setup_boot_APIC_clock(void)
 
     calibrate_APIC_clock();
 
+    if ( tdt_enable && boot_cpu_has(X86_FEATURE_TSC_DEADLINE) )
+    {
+        printk(KERN_DEBUG "TSC deadline timer enabled\n");
+        tdt_enabled = 1;
+    }
+
     setup_APIC_timer();
     
     local_irq_restore(flags);
@@ -1360,10 +1382,24 @@ int reprogram_timer(s_time_t timeout)
     if ( !cpu_has_apic )
         return 1;
 
-    if ( timeout && ((expire = timeout - NOW()) > 0) )
-        apic_tmict = min_t(u64, (bus_scale * expire) >> 18, UINT_MAX);
-
-    apic_write(APIC_TMICT, (unsigned long)apic_tmict);
+    if ( tdt_enabled )
+    {
+        u64 tsc = 0;
+
+        if ( timeout )
+            tsc = stime2tsc(timeout);
+
+        wrmsrl(MSR_IA32_TSC_DEADLINE, tsc);
+
+        return 1;
+    }
+    else
+    {
+        if ( timeout && ((expire = timeout - NOW()) > 0) )
+            apic_tmict = min_t(u64, (bus_scale * expire) >> 18, UINT_MAX);
+
+        apic_write(APIC_TMICT, (unsigned long)apic_tmict);
+    }
 
     return apic_tmict || !timeout;
 }
diff -r 0dc0bc411035 xen/arch/x86/time.c
--- a/xen/arch/x86/time.c       Thu Oct 21 18:51:36 2010 +0100
+++ b/xen/arch/x86/time.c       Fri Oct 29 19:30:33 2010 +0800
@@ -662,26 +662,31 @@ static void __init init_platform_timer(v
            freq_string(pts->frequency), pts->name);
 }
 
-void cstate_restore_tsc(void)
+u64 stime2tsc(s_time_t stime)
 {
     struct cpu_time *t;
     struct time_scale sys_to_tsc;
     s_time_t stime_delta;
-    u64 new_tsc;
-
+    u64 tsc;
+
+    t = &this_cpu(cpu_time);
+    sys_to_tsc = scale_reciprocal(t->tsc_scale);
+
+    stime_delta = stime - t->stime_local_stamp;
+    if ( stime_delta < 0 )
+        stime_delta = 0;
+
+    tsc = t->local_tsc_stamp + scale_delta(stime_delta, &sys_to_tsc);
+
+    return tsc;
+}
+
+void cstate_restore_tsc(void)
+{
     if ( boot_cpu_has(X86_FEATURE_NONSTOP_TSC) )
         return;
 
-    t = &this_cpu(cpu_time);
-    sys_to_tsc = scale_reciprocal(t->tsc_scale);
-
-    stime_delta = read_platform_stime() - t->stime_master_stamp;
-    if ( stime_delta < 0 )
-        stime_delta = 0;
-
-    new_tsc = t->local_tsc_stamp + scale_delta(stime_delta, &sys_to_tsc);
-
-    write_tsc(new_tsc);
+    write_tsc(stime2tsc(read_platform_stime()));
 }
 
 /***************************************************************************
diff -r 0dc0bc411035 xen/include/asm-x86/cpufeature.h
--- a/xen/include/asm-x86/cpufeature.h  Thu Oct 21 18:51:36 2010 +0100
+++ b/xen/include/asm-x86/cpufeature.h  Fri Oct 29 19:30:33 2010 +0800
@@ -99,6 +99,7 @@
 #define X86_FEATURE_SSE4_2     (4*32+20) /* Streaming SIMD Extensions 4.2 */
 #define X86_FEATURE_X2APIC     (4*32+21) /* Extended xAPIC */
 #define X86_FEATURE_POPCNT     (4*32+23) /* POPCNT instruction */
+#define X86_FEATURE_TSC_DEADLINE (4*32+24) /* "tdt" TSC Deadline Timer */
 #define X86_FEATURE_XSAVE      (4*32+26) /* XSAVE/XRSTOR/XSETBV/XGETBV */
 #define X86_FEATURE_OSXSAVE    (4*32+27) /* OSXSAVE */
 #define X86_FEATURE_HYPERVISOR (4*32+31) /* Running under some hypervisor */
diff -r 0dc0bc411035 xen/include/asm-x86/msr-index.h
--- a/xen/include/asm-x86/msr-index.h   Thu Oct 21 18:51:36 2010 +0100
+++ b/xen/include/asm-x86/msr-index.h   Fri Oct 29 19:30:33 2010 +0800
@@ -327,6 +327,8 @@
 #define MSR_IA32_MISC_ENABLE_MONITOR_ENABLE (1<<18)
 #define MSR_IA32_MISC_ENABLE_LIMIT_CPUID  (1<<22)
 #define MSR_IA32_MISC_ENABLE_XTPR_DISABLE (1<<23)
+
+#define MSR_IA32_TSC_DEADLINE          0x000006E0
 
 /* Intel Model 6 */
 #define MSR_P6_EVNTSEL0                        0x00000186
diff -r 0dc0bc411035 xen/include/xen/time.h
--- a/xen/include/xen/time.h    Thu Oct 21 18:51:36 2010 +0100
+++ b/xen/include/xen/time.h    Fri Oct 29 19:30:33 2010 +0800
@@ -31,6 +31,7 @@ typedef s64 s_time_t;
 typedef s64 s_time_t;
 
 s_time_t get_s_time(void);
+u64 stime2tsc(s_time_t stime);
 unsigned long get_localtime(struct domain *d);
 
 struct tm {

tdt-host-support.patch
Description: tdt-host-support.patch

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