diff options
Diffstat (limited to 'include/vdso/helpers.h')
| -rw-r--r-- | include/vdso/helpers.h | 31 |
1 files changed, 30 insertions, 1 deletions
diff --git a/include/vdso/helpers.h b/include/vdso/helpers.h index 1a5ee9d9052c..a3bf4f1c0d37 100644 --- a/include/vdso/helpers.h +++ b/include/vdso/helpers.h @@ -6,6 +6,13 @@ #include <asm/barrier.h> #include <vdso/datapage.h> +#include <vdso/processor.h> +#include <vdso/clocksource.h> + +static __always_inline bool vdso_is_timens_clock(const struct vdso_clock *vc) +{ + return IS_ENABLED(CONFIG_TIME_NS) && vc->clock_mode == VDSO_CLOCKMODE_TIMENS; +} static __always_inline u32 vdso_read_begin(const struct vdso_clock *vc) { @@ -18,6 +25,28 @@ static __always_inline u32 vdso_read_begin(const struct vdso_clock *vc) return seq; } +/* + * Variant of vdso_read_begin() to handle VDSO_CLOCKMODE_TIMENS. + * + * Time namespace enabled tasks have a special VVAR page installed which has + * vc->seq set to 1 and vc->clock_mode set to VDSO_CLOCKMODE_TIMENS. For non + * time namespace affected tasks this does not affect performance because if + * vc->seq is odd, i.e. a concurrent update is in progress the extra check for + * vc->clock_mode is just a few extra instructions while spin waiting for + * vc->seq to become even again. + */ +static __always_inline bool vdso_read_begin_timens(const struct vdso_clock *vc, u32 *seq) +{ + while (unlikely((*seq = READ_ONCE(vc->seq)) & 1)) { + if (vdso_is_timens_clock(vc)) + return true; + cpu_relax(); + } + smp_rmb(); + + return false; +} + static __always_inline u32 vdso_read_retry(const struct vdso_clock *vc, u32 start) { @@ -25,7 +54,7 @@ static __always_inline u32 vdso_read_retry(const struct vdso_clock *vc, smp_rmb(); seq = READ_ONCE(vc->seq); - return seq != start; + return unlikely(seq != start); } static __always_inline void vdso_write_seq_begin(struct vdso_clock *vc) |