Re: a joint letter on low latency and Linux

[Andre Hedrick]

/*
 * Timeouts for various operations:
 */
#define WAIT_DRQ        (5*HZ/100)      /* 50msec - spec allows up to 20ms */
#ifdef CONFIG_APM
#define WAIT_READY      (5*HZ)          /* 5sec - some laptops are very slow */
#else
#define WAIT_READY      (3*HZ/100)      /* 30msec - should be instantaneous */
#endif /* CONFIG_APM */
#define WAIT_PIDENTIFY  (10*HZ) /* 10sec  - should be less than 3ms (?)
                                            if all ATAPI CD is closed at boot */
#define WAIT_WORSTCASE  (30*HZ) /* 30sec  - worst case when spinning up */
#define WAIT_CMD        (10*HZ) /* 10sec  - maximum wait for an IRQ to happen */
#define WAIT_MIN_SLEEP  (2*HZ/100)      /* 20msec - minimum sleep time */

Look, I do not care what HZ is used, I have a fixed timeout base that I
have to work with in order for ATA/ATAPI to work period.  Blowing these
values will be a damn excellent way to crap out the entire sub-system.

This is my concern.  I do not care how we address it, I have to be able to
clock intervals in a predictable fashion.

Cheers,

Andre Hedrick
The Linux ATA/IDE guy