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cam: add hw.cam.iosched.read_bias

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Allow a global setting for the read_bias for the dynamic io
scheduler. This allows global policy to be set, in addition to the
existing per-drive policy. kern.cam.iosched.read_bias is a new tunable.

Sponsored by:		Netflix
Reviewed by:		chs
Differential Revision:	https://reviews.freebsd.org/D34365
This commit is contained in:
Warner Losh 2022-05-01 11:18:27 -06:00
parent b65803ba57
commit d592c0db8b
1 changed files with 11 additions and 2 deletions
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13
sys/cam/cam_iosched.c
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@ -139,6 +139,15 @@ SYSCTL_INT(_kern_cam_iosched, OID_AUTO, buckets, CTLFLAG_RD,
&lat_buckets, LAT_BUCKETS,
"Total number of latency buckets published");
/*
* Read bias: how many reads do we favor before scheduling a write
* when we have a choice.
*/
static int default_read_bias = 0;
SYSCTL_INT(_kern_cam_iosched, OID_AUTO, read_bias, CTLFLAG_RWTUN,
&default_read_bias, 0,
"Default read bias for new devices.");
struct iop_stats;
struct cam_iosched_softc;
@ -1149,7 +1158,7 @@ cam_iosched_init(struct cam_iosched_softc **iscp, struct cam_periph *periph)
#ifdef CAM_IOSCHED_DYNAMIC
if (do_dynamic_iosched) {
bioq_init(&(*iscp)->write_queue);
(*iscp)->read_bias = 0;
(*iscp)->read_bias = default_read_bias;
(*iscp)->current_read_bias = 0;
(*iscp)->quanta = min(hz, 200);
cam_iosched_iop_stats_init(*iscp, &(*iscp)->read_stats);
@ -1234,7 +1243,7 @@ void cam_iosched_sysctl_init(struct cam_iosched_softc *isc,
SYSCTL_ADD_INT(ctx, n,
OID_AUTO, "read_bias", CTLFLAG_RW,
&isc->read_bias, 0,
&isc->read_bias, default_read_bias,
"How biased towards read should we be independent of limits");
SYSCTL_ADD_PROC(ctx, n,