Reduce overhead of entropy collection

- move harvest mask check inline
- move harvest mask to frequently_read out of actively
  modified cache line
- disable ether_input collection and describe its limitations
  in NOTES

Typically entropy collection in ether_input was stirring zero
in to the entropy pool while at the same time greatly reducing
max pps. This indicates that perhaps we should more closely
scrutinize how much entropy we're getting from a given source
as well as what our actual entropy collection needs are for
seeding Yarrow.

Reviewed by: cem, gallatin, delphij
Approved by: secteam
Differential Revision: https://reviews.freebsd.org/D15526

1 files changed, 19 insertions, 24 deletions

diff --git a/sys/dev/random/random_harvestq.c b/sys/dev/random/random_harvestq.c
index 840932ebfbb8..f064ab02b358 100644
--- a/sys/dev/random/random_harvestq.c
+++ b/sys/dev/random/random_harvestq.c
@@ -80,6 +80,12 @@ static struct sysctl_ctx_list random_clist;
 /* 1 to let the kernel thread run, 0 to terminate, -1 to mark completion */
 volatile int random_kthread_control;
 
+
+/* Allow the sysadmin to select the broad category of
+ * entropy types to harvest.
+ */
+__read_frequently u_int hc_source_mask;
+
 /*
  * Put all the harvest queue context stuff in one place.
  * this make is a bit easier to lock and protect.
@@ -93,10 +99,6 @@ static struct harvest_context {
 	u_int hc_destination[ENTROPYSOURCE];
 	/* The context of the kernel thread processing harvested entropy */
 	struct proc *hc_kthread_proc;
-	/* Allow the sysadmin to select the broad category of
-	 * entropy types to harvest.
-	 */
-	u_int hc_source_mask;
 	/*
 	 * Lockless ring buffer holding entropy events
 	 * If ring.in == ring.out,
@@ -248,7 +250,7 @@ random_check_uint_harvestmask(SYSCTL_HANDLER_ARGS)
 	int error;
 	u_int value, orig_value;
 
-	orig_value = value = harvest_context.hc_source_mask;
+	orig_value = value = hc_source_mask;
 	error = sysctl_handle_int(oidp, &value, 0, req);
 	if (error != 0 || req->newptr == NULL)
 		return (error);
@@ -259,7 +261,7 @@ random_check_uint_harvestmask(SYSCTL_HANDLER_ARGS)
 	/*
 	 * Disallow userspace modification of pure entropy sources.
 	 */
-	harvest_context.hc_source_mask = (value & ~RANDOM_HARVEST_PURE_MASK) |
+	hc_source_mask = (value & ~RANDOM_HARVEST_PURE_MASK) |
 	    (orig_value & RANDOM_HARVEST_PURE_MASK);
 	return (0);
 }
@@ -275,7 +277,7 @@ random_print_harvestmask(SYSCTL_HANDLER_ARGS)
 	if (error == 0) {
 		sbuf_new_for_sysctl(&sbuf, NULL, 128, req);
 		for (i = ENTROPYSOURCE - 1; i >= 0; i--)
-			sbuf_cat(&sbuf, (harvest_context.hc_source_mask & (1 << i)) ? "1" : "0");
+			sbuf_cat(&sbuf, (hc_source_mask & (1 << i)) ? "1" : "0");
 		error = sbuf_finish(&sbuf);
 		sbuf_delete(&sbuf);
 	}
@@ -322,13 +324,13 @@ random_print_harvestmask_symbolic(SYSCTL_HANDLER_ARGS)
 		sbuf_new_for_sysctl(&sbuf, NULL, 128, req);
 		for (i = ENTROPYSOURCE - 1; i >= 0; i--) {
 			if (i >= RANDOM_PURE_START &&
-			    (harvest_context.hc_source_mask & (1 << i)) == 0)
+			    (hc_source_mask & (1 << i)) == 0)
 				continue;
 			if (!first)
 				sbuf_cat(&sbuf, ",");
-			sbuf_cat(&sbuf, !(harvest_context.hc_source_mask & (1 << i)) ? "[" : "");
+			sbuf_cat(&sbuf, !(hc_source_mask & (1 << i)) ? "[" : "");
 			sbuf_cat(&sbuf, random_source_descr[i]);
-			sbuf_cat(&sbuf, !(harvest_context.hc_source_mask & (1 << i)) ? "]" : "");
+			sbuf_cat(&sbuf, !(hc_source_mask & (1 << i)) ? "]" : "");
 			first = false;
 		}
 		error = sbuf_finish(&sbuf);
@@ -347,7 +349,7 @@ random_harvestq_init(void *unused __unused)
 	    SYSCTL_STATIC_CHILDREN(_kern_random),
 	    OID_AUTO, "harvest", CTLFLAG_RW, 0,
 	    "Entropy Device Parameters");
-	harvest_context.hc_source_mask = RANDOM_HARVEST_EVERYTHING_MASK;
+	hc_source_mask = RANDOM_HARVEST_EVERYTHING_MASK;
 	SYSCTL_ADD_PROC(&random_clist,
 	    SYSCTL_CHILDREN(random_sys_o),
 	    OID_AUTO, "mask", CTLTYPE_UINT | CTLFLAG_RW,
@@ -448,14 +450,13 @@ SYSUNINIT(random_device_h_init, SI_SUB_RANDOM, SI_ORDER_SECOND, random_harvestq_
  * read which can be quite expensive.
  */
 void
-random_harvest_queue(const void *entropy, u_int size, u_int bits, enum random_entropy_source origin)
+random_harvest_queue_(const void *entropy, u_int size, u_int bits,
+	enum random_entropy_source origin)
 {
 	struct harvest_event *event;
 	u_int ring_in;
 
 	KASSERT(origin >= RANDOM_START && origin < ENTROPYSOURCE, ("%s: origin %d invalid\n", __func__, origin));
-	if (!(harvest_context.hc_source_mask & (1 << origin)))
-		return;
 	RANDOM_HARVEST_LOCK();
 	ring_in = (harvest_context.hc_entropy_ring.in + 1)%RANDOM_RING_MAX;
 	if (ring_in != harvest_context.hc_entropy_ring.out) {
@@ -486,14 +487,10 @@ random_harvest_queue(const void *entropy, u_int size, u_int bits, enum random_en
  * This is the right place for high-rate harvested data.
  */
 void
-random_harvest_fast(const void *entropy, u_int size, u_int bits, enum random_entropy_source origin)
+random_harvest_fast_(const void *entropy, u_int size, u_int bits)
 {
 	u_int pos;
 
-	KASSERT(origin >= RANDOM_START && origin < ENTROPYSOURCE, ("%s: origin %d invalid\n", __func__, origin));
-	/* XXX: FIX!! The above KASSERT is BS. Right now we ignore most structure and just accumulate the supplied data */
-	if (!(harvest_context.hc_source_mask & (1 << origin)))
-		return;
 	pos = harvest_context.hc_entropy_fast_accumulator.pos;
 	harvest_context.hc_entropy_fast_accumulator.buf[pos] ^= jenkins_hash(entropy, size, (uint32_t)get_cyclecount());
 	harvest_context.hc_entropy_fast_accumulator.pos = (pos + 1)%RANDOM_ACCUM_MAX;
@@ -506,13 +503,11 @@ random_harvest_fast(const void *entropy, u_int size, u_int bits, enum random_ent
  * (e.g.) booting when initial entropy is being gathered.
  */
 void
-random_harvest_direct(const void *entropy, u_int size, u_int bits, enum random_entropy_source origin)
+random_harvest_direct_(const void *entropy, u_int size, u_int bits, enum random_entropy_source origin)
 {
 	struct harvest_event event;
 
 	KASSERT(origin >= RANDOM_START && origin < ENTROPYSOURCE, ("%s: origin %d invalid\n", __func__, origin));
-	if (!(harvest_context.hc_source_mask & (1 << origin)))
-		return;
 	size = MIN(size, sizeof(event.he_entropy));
 	event.he_somecounter = (uint32_t)get_cyclecount();
 	event.he_size = size;
@@ -528,14 +523,14 @@ void
 random_harvest_register_source(enum random_entropy_source source)
 {
 
-	harvest_context.hc_source_mask |= (1 << source);
+	hc_source_mask |= (1 << source);
 }
 
 void
 random_harvest_deregister_source(enum random_entropy_source source)
 {
 
-	harvest_context.hc_source_mask &= ~(1 << source);
+	hc_source_mask &= ~(1 << source);
 }
 
 MODULE_VERSION(random_harvestq, 1);