[PATCH] [6/20] x86: Remove get_cycles_sync

Andi Kleen
2008-01-03T00:51:53Z

And replace with nsec_barrier() as needed which has the same effect
of preventing unnecessary speculation around RDTSC.

For the standard gtod() like calls the previous patch already added the
necessary barriers

Signed-off-by: Andi Kleen <ak@suse.de>

---
arch/x86/kernel/time_64.c | 4 +++-
arch/x86/kernel/tsc_64.c | 17 +++++++++++------
arch/x86/kernel/tsc_sync.c | 6 ++++--
include/asm-x86/tsc.h | 44 ++++----------------------------------------
4 files changed, 22 insertions(+), 49 deletions(-)

Index: linux/arch/x86/kernel/time_64.c
===================================================================
--- linux.orig/arch/x86/kernel/time_64.c
+++ linux/arch/x86/kernel/time_64.c
@@ -81,9 +81,11 @@ unsigned long __init native_calculate_cp
wrmsrl(MSR_K7_PERFCTR0 + i, 0);
wrmsrl(MSR_K7_EVNTSEL0 + i, 1 << 22 | 3 << 16 | 0x76);
rdtscl(tsc_start);
+ nsec_barrier();
do {
rdmsrl(MSR_K7_PERFCTR0 + i, pmc_now);
- tsc_now = get_cycles_sync();
+ nsec_barrier();
+ tsc_now = get_cycles();
} while ((tsc_now - tsc_start) < TICK_COUNT);

local_irq_restore(flags);
Index: linux/arch/x86/kernel/tsc_64.c
===================================================================
--- linux.orig/arch/x86/kernel/tsc_64.c
+++ linux/arch/x86/kernel/tsc_64.c
@@ -181,12 +181,14 @@ static unsigned long __init tsc_read_ref
int i;

for (i = 0; i < MAX_RETRIES; i++) {
- t1 = get_cycles_sync();
+ nsec_barrier();
+ t1 = get_cycles();
if (hpet)
*hpet = hpet_readl(HPET_COUNTER) & 0xFFFFFFFF;
else
*pm = acpi_pm_read_early();
- t2 = get_cycles_sync();
+ nsec_barrier();
+ t2 = get_cycles();
if ((t2 - t1) < SMI_TRESHOLD)
return t2;
}
@@ -210,9 +212,11 @@ void __init tsc_calibrate(void)
outb(0xb0, 0x43);
outb((CLOCK_TICK_RATE / (1000 / 50)) & 0xff, 0x42);
outb((CLOCK_TICK_RATE / (1000 / 50)) >> 8, 0x42);
- tr1 = get_cycles_sync();
+ tr1 = get_cycles();
+ nsec_barrier();
while ((inb(0x61) & 0x20) == 0);
- tr2 = get_cycles_sync();
+ nsec_barrier();
+ tr2 = get_cycles();

tsc2 = tsc_read_refs(&pm2, hpet ? &hpet2 : NULL);

@@ -298,15 +302,16 @@ __setup("notsc", notsc_setup);

/* clock source code: */
+/* Caller must do nsec_barrier()s */
static cycle_t read_tsc(void)
{
- cycle_t ret = (cycle_t)get_cycles_sync();
+ cycle_t ret = (cycle_t)get_cycles();
return ret;
}

static cycle_t __vsyscall_fn vread_tsc(void)
{
- cycle_t ret = (cycle_t)vget_cycles_sync();
+ cycle_t ret = (cycle_t)vget_cycles();
return ret;
}

Index: linux/include/asm-x86/tsc.h
===================================================================
--- linux.orig/include/asm-x86/tsc.h
+++ linux/include/asm-x86/tsc.h
@@ -36,61 +36,25 @@ static inline cycles_t get_cycles(void)
return ret;
}

-/* Like get_cycles, but make sure the CPU is synchronized. */
-static __always_inline cycles_t __get_cycles_sync(void)
-{
- unsigned long long ret;
- unsigned eax, edx;
-
- /*
- * Use RDTSCP if possible; it is guaranteed to be synchronous
- * and doesn't cause a VMEXIT on Hypervisors
- */
- alternative_io(ASM_NOP3, ".byte 0x0f,0x01,0xf9", X86_FEATURE_RDTSCP,
- ASM_OUTPUT2("=a" (eax), "=d" (edx)),
- "a" (0U), "d" (0U) : "ecx", "memory");
- ret = (((unsigned long long)edx) << 32) | ((unsigned long long)eax);
- if (ret)
- return ret;
-
- /*
- * Don't do an additional sync on CPUs where we know
- * RDTSC is already synchronous:
- */
- alternative_io("cpuid", ASM_NOP2, X86_FEATURE_SYNC_RDTSC,
- "=a" (eax), "0" (1) : "ebx","ecx","edx","memory");
-
- return 0;
-}
-
-static __always_inline cycles_t get_cycles_sync(void)
-{
- unsigned long long ret;
- ret = __get_cycles_sync();
- if (!ret)
- rdtscll(ret);
- return ret;
-}
-
#ifdef CONFIG_PARAVIRT
/*
* For paravirt guests, some functionalities are executed through function
* pointers in the various pvops structures.
* These function pointers exist inside the kernel and can not
* be accessed by user space. To avoid this, we make a copy of the
- * get_cycles_sync (called in kernel) but force the use of native_read_tsc.
+ * get_cycles (called in kernel) but force the use of native_read_tsc.
* Ideally, the guest should set up it's own clock and vread
*/
-static __always_inline long long vget_cycles_sync(void)
+static __always_inline long long vget_cycles(void)
{
unsigned long long ret;
- ret = __get_cycles_sync();
+ ret = get_cycles();
if (!ret)
ret = native_read_tsc();
return ret;
}
#else
-# define vget_cycles_sync() get_cycles_sync()
+# define vget_cycles() get_cycles()
#endif

extern void tsc_init(void);
Index: linux/arch/x86/kernel/tsc_sync.c
===================================================================
--- linux.orig/arch/x86/kernel/tsc_sync.c
+++ linux/arch/x86/kernel/tsc_sync.c
@@ -46,7 +46,8 @@ static __cpuinit void check_tsc_warp(voi
cycles_t start, now, prev, end;
int i;

- start = get_cycles_sync();
+ start = get_cycles();
+ nsec_barrier();
/*
* The measurement runs for 20 msecs:
*/
@@ -61,7 +62,8 @@ static __cpuinit void check_tsc_warp(voi
*/
__raw_spin_lock(&sync_lock);
prev = last_tsc;
- now = get_cycles_sync();
+ nsec_barrier();
+ now = get_cycles();
last_tsc = now;
__raw_spin_unlock(&sync_lock);