x86: vdso: pvclock gettime support

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@redhat.com>
This commit is contained in:
Marcelo Tosatti 2012-11-27 23:28:57 -02:00
parent 3dc4f7cfb7
commit 51c19b4f59
3 changed files with 101 additions and 11 deletions

View File

@ -33,6 +33,26 @@ extern void map_vsyscall(void);
*/
extern bool emulate_vsyscall(struct pt_regs *regs, unsigned long address);
#ifdef CONFIG_X86_64
#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 /* CONFIG_X86_64 */
#endif /* __KERNEL__ */
#endif /* _ASM_X86_VSYSCALL_H */

View File

@ -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(struct timeval *tv, struct timezone *tz)
}
notrace static inline u64 vgetsns(void)
notrace static inline u64 vgetsns(int *mode)
{
long v;
cycles_t cycles;
@ -88,6 +159,10 @@ notrace static inline u64 vgetsns(void)
cycles = vread_tsc();
else if (gtod->clock.vclock_mode == VCLOCK_HPET)
cycles = vread_hpet();
#ifdef CONFIG_PARAVIRT_CLOCK
else if (gtod->clock.vclock_mode == VCLOCK_PVCLOCK)
cycles = vread_pvclock(mode);
#endif
else
return 0;
v = (cycles - gtod->clock.cycle_last) & gtod->clock.mask;
@ -107,7 +182,7 @@ notrace static int __always_inline do_realtime(struct timespec *ts)
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(&gtod->seq, seq)));
@ -127,7 +202,7 @@ notrace static int do_monotonic(struct timespec *ts)
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(&gtod->seq, seq)));
timespec_add_ns(ts, ns);

View File

@ -17,15 +17,10 @@ __vdso_getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *unused)
{
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;