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Diffstat (limited to 'drivers/md/dm-path-selector.h')
| -rw-r--r-- | drivers/md/dm-path-selector.h | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/drivers/md/dm-path-selector.h b/drivers/md/dm-path-selector.h index c47bc0e20275..83cac2b04b66 100644 --- a/drivers/md/dm-path-selector.h +++ b/drivers/md/dm-path-selector.h @@ -26,11 +26,26 @@ struct path_selector { void *context; }; +/* + * If a path selector uses this flag, a high resolution timer is used + * (via ktime_get_ns) to account for IO start time in BIO-based mpath. + * This improves performance of some path selectors (i.e. HST), in + * exchange for slightly higher overhead when submitting the BIO. + * The extra cost is usually offset by improved path selection for + * some benchmarks. + * + * This has no effect for request-based mpath, since it already uses a + * higher precision timer by default. + */ +#define DM_PS_USE_HR_TIMER 0x00000001 +#define dm_ps_use_hr_timer(type) ((type)->features & DM_PS_USE_HR_TIMER) + /* Information about a path selector type */ struct path_selector_type { char *name; struct module *module; + unsigned int features; unsigned int table_args; unsigned int info_args; |