Improve performance of time system calls when using Linux pvclock,
by reading time info from fixmap visible copy of pvclock data.
Originally from Jeremy Fitzhardinge.
Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Index: vsyscall/arch/x86/vdso/vclock_gettime.c
===================================================================
--- vsyscall.orig/arch/x86/vdso/vclock_gettime.c
+++ vsyscall/arch/x86/vdso/vclock_gettime.c
@@ -22,6 +22,7 @@
#include <asm/hpet.h>
#include <asm/unistd.h>
#include <asm/io.h>
+#include <asm/pvclock.h>
#define gtod (&VVAR(vsyscall_gtod_data))
@@ -62,6 +63,76 @@ static notrace cycle_t vread_hpet(void)
return readl((const void __iomem *)fix_to_virt(VSYSCALL_HPET) + 0xf0);
}
+#ifdef CONFIG_PARAVIRT_CLOCK
+
+static notrace const struct pvclock_vsyscall_time_info *get_pvti(int cpu)
+{
+ const struct pvclock_vsyscall_time_info *pvti_base;
+ int idx = cpu / (PAGE_SIZE/PVTI_SIZE);
+ int offset = cpu % (PAGE_SIZE/PVTI_SIZE);
+
+ BUG_ON(PVCLOCK_FIXMAP_BEGIN + idx > PVCLOCK_FIXMAP_END);
+
+ pvti_base = (struct pvclock_vsyscall_time_info *)
+ __fix_to_virt(PVCLOCK_FIXMAP_BEGIN+idx);
+
+ return &pvti_base[offset];
+}
+
+static notrace cycle_t vread_pvclock(int *mode)
+{
+ const struct pvclock_vsyscall_time_info *pvti;
+ cycle_t ret;
+ u64 last;
+ u32 version;
+ u32 migrate_count;
+ u8 flags;
+ unsigned cpu, cpu1;
+
+
+ /*
+ * When looping to get a consistent (time-info, tsc) pair, we
+ * also need to deal with the possibility we can switch vcpus,
+ * so make sure we always re-fetch time-info for the current vcpu.
+ */
+ do {
+ cpu = __getcpu() & VGETCPU_CPU_MASK;
+ /* TODO: We can put vcpu id into higher bits of pvti.version.
+ * This will save a couple of cycles by getting rid of
+ * __getcpu() calls (Gleb).
+ */
+
+ pvti = get_pvti(cpu);
+
+ migrate_count = pvti->migrate_count;
+
+ version = __pvclock_read_cycles(&pvti->pvti, &ret, &flags);
+
+ /*
+ * Test we're still on the cpu as well as the version.
+ * We could have been migrated just after the first
+ * vgetcpu but before fetching the version, so we
+ * wouldn't notice a version change.
+ */
+ cpu1 = __getcpu() & VGETCPU_CPU_MASK;
+ } while (unlikely(cpu != cpu1 ||
+ (pvti->pvti.version & 1) ||
+ pvti->pvti.version != version ||
+ pvti->migrate_count != migrate_count));
+
+ if (unlikely(!(flags & PVCLOCK_TSC_STABLE_BIT)))
+ *mode = VCLOCK_NONE;
+
+ /* refer to tsc.c read_tsc() comment for rationale */
+ last = VVAR(vsyscall_gtod_data).clock.cycle_last;
+
+ if (likely(ret >= last))
+ return ret;
+
+ return last;
+}
+#endif
+
notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
{
long ret;
@@ -80,7 +151,7 @@ notrace static long vdso_fallback_gtod(s
}
-notrace static inline u64 vgetsns(void)
+notrace static inline u64 vgetsns(int *mode)
{
long v;
cycles_t cycles;
@@ -88,6 +159,8 @@ notrace static inline u64 vgetsns(void)
cycles = vread_tsc();
else if (gtod->clock.vclock_mode == VCLOCK_HPET)
cycles = vread_hpet();
+ else if (gtod->clock.vclock_mode == VCLOCK_PVCLOCK)
+ cycles = vread_pvclock(mode);
else
return 0;
v = (cycles - gtod->clock.cycle_last) & gtod->clock.mask;
@@ -107,7 +180,7 @@ notrace static int __always_inline do_re
mode = gtod->clock.vclock_mode;
ts->tv_sec = gtod->wall_time_sec;
ns = gtod->wall_time_snsec;
- ns += vgetsns();
+ ns += vgetsns(&mode);
ns >>= gtod->clock.shift;
} while (unlikely(read_seqcount_retry(>od->seq, seq)));
@@ -127,7 +200,7 @@ notrace static int do_monotonic(struct t
mode = gtod->clock.vclock_mode;
ts->tv_sec = gtod->monotonic_time_sec;
ns = gtod->monotonic_time_snsec;
- ns += vgetsns();
+ ns += vgetsns(&mode);
ns >>= gtod->clock.shift;
} while (unlikely(read_seqcount_retry(>od->seq, seq)));
timespec_add_ns(ts, ns);
Index: vsyscall/arch/x86/include/asm/vsyscall.h
===================================================================
--- vsyscall.orig/arch/x86/include/asm/vsyscall.h
+++ vsyscall/arch/x86/include/asm/vsyscall.h
@@ -33,6 +33,23 @@ extern void map_vsyscall(void);
*/
extern bool emulate_vsyscall(struct pt_regs *regs, unsigned long address);
+#define VGETCPU_CPU_MASK 0xfff
+
+static inline unsigned int __getcpu(void)
+{
+ unsigned int p;
+
+ if (VVAR(vgetcpu_mode) == VGETCPU_RDTSCP) {
+ /* Load per CPU data from RDTSCP */
+ native_read_tscp(&p);
+ } else {
+ /* Load per CPU data from GDT */
+ asm("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG));
+ }
+
+ return p;
+}
+
#endif /* __KERNEL__ */
#endif /* _ASM_X86_VSYSCALL_H */
Index: vsyscall/arch/x86/vdso/vgetcpu.c
===================================================================
--- vsyscall.orig/arch/x86/vdso/vgetcpu.c
+++ vsyscall/arch/x86/vdso/vgetcpu.c
@@ -17,15 +17,10 @@ __vdso_getcpu(unsigned *cpu, unsigned *n
{
unsigned int p;
- if (VVAR(vgetcpu_mode) == VGETCPU_RDTSCP) {
- /* Load per CPU data from RDTSCP */
- native_read_tscp(&p);
- } else {
- /* Load per CPU data from GDT */
- asm("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG));
- }
+ p = __getcpu();
+
if (cpu)
- *cpu = p & 0xfff;
+ *cpu = p & VGETCPU_CPU_MASK;
if (node)
*node = p >> 12;
return 0;
--
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