77  * For an EMA, with an alpha of alpha, we know
78  * 	alpha = 2 / (N + 1)
80  * 	N = 1 + (2 / alpha)
85  *	alpha_bits = -log_2(alpha)
86  *	alpha = 2^-alpha_bits
94  * Note: See computation of EMA and EMVAR for acceptable ranges of alpha.
99     "Bits in EMA's alpha.");
307 	int		alpha;  member
669 	clp->alpha = 20;			/* Alpha == gain. 20 = .2 */  in cam_iosched_cl_init()
711 		 * is why we use a relatively low alpha of between .1 and .25 to  in cam_iosched_cl_maybe_steer()
726 			    (100 + clp->alpha) / 100;	/* Scale up */  in cam_iosched_cl_maybe_steer()
729 			    (100 - clp->alpha) / 100;	/* Scale down */  in cam_iosched_cl_maybe_steer()
1141 	    OID_AUTO, "alpha", CTLFLAG_RW,  in cam_iosched_cl_sysctl_init()
1142 	    &clp->alpha, 0,  in cam_iosched_cl_sysctl_init()
1143 	    "Alpha for PLL (x100) aka gain");  in cam_iosched_cl_sysctl_init()
1989 	 * Classic exponentially decaying average with a tiny alpha  in cam_iosched_update()
1993 	 * ema_t = y_t * alpha + ema_t-1 * (1 - alpha)		[nist]  in cam_iosched_update()
1994 	 * ema_t = y_t * alpha + ema_t-1 - alpha * ema_t-1  in cam_iosched_update()
1995 	 * ema_t = alpha * y_t - alpha * ema_t-1 + ema_t-1  in cam_iosched_update()
1996 	 * alpha = 1 / (1 << alpha_bits)  in cam_iosched_update()
1997 	 * sub e == ema_t-1, b == 1/alpha (== 1 << alpha_bits), d == y_t - ema_t-1  in cam_iosched_update()
2002 	 * Since alpha is a power of two, we can compute this w/o any mult or  in cam_iosched_update()
2007 	 *	emvar_t = (1 - alpha) * (emavar_t-1 + diff_t^2 * alpha)  in cam_iosched_update()
2008 	 *	  = emavar_t-1 - alpha * emavar_t-1 + delta_t^2 * alpha - (delta_t * alpha)^2  in cam_iosched_update()
2009 	 * sub b == 1/alpha (== 1 << alpha_bits), e == emavar_t-1, d = delta_t^2  in cam_iosched_update()
2017 	 *	  implementation defined. You can change the right shifts to / (1LL << alpha).  in cam_iosched_update()
2019 	 *	  for emvar. This puts a ceiling of 13 bits on alpha since we need a  in cam_iosched_update()
2021 	 *	o We mitigate alpha issues by never setting it too high.  in cam_iosched_update()
2038 	 * assume alpha=9. 10 or 11 are ok, but we start to run into issues at 12,  in cam_iosched_update()