random: remove ifdef'd out interrupt bench

With tools like kbench9000 giving more finegrained responses, and this
basically never having been used ever since it was initially added,
let's just get rid of this. There *is* still work to be done on the
interrupt handler, but this really isn't the way it's being developed.

Cc: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

Documentation/admin-guide/sysctl/kernel.rst

@@ -1041,15 +1041,6 @@ This is a directory, with the following entries:
   are woken up. This file is writable for compatibility purposes, but
   writing to it has no effect on any RNG behavior.
 
-If ``drivers/char/random.c`` is built with ``ADD_INTERRUPT_BENCH``
-defined, these additional entries are present:
-
-* ``add_interrupt_avg_cycles``: the average number of cycles between
-  interrupts used to feed the pool;
-
-* ``add_interrupt_avg_deviation``: the standard deviation seen on the
-  number of cycles between interrupts used to feed the pool.
-
 
 randomize_va_space
 ==================

drivers/char/random.c

@@ -240,8 +240,6 @@
 #define CREATE_TRACE_POINTS
 #include <trace/events/random.h>
 
-/* #define ADD_INTERRUPT_BENCH */
-
 enum {
 	POOL_BITS = BLAKE2S_HASH_SIZE * 8,
 	POOL_MIN_BITS = POOL_BITS /* No point in settling for less. */
@@ -808,27 +806,6 @@ EXPORT_SYMBOL_GPL(add_input_randomness);
 
 static DEFINE_PER_CPU(struct fast_pool, irq_randomness);
 
-#ifdef ADD_INTERRUPT_BENCH
-static unsigned long avg_cycles, avg_deviation;
-
-#define AVG_SHIFT 8 /* Exponential average factor k=1/256 */
-#define FIXED_1_2 (1 << (AVG_SHIFT - 1))
-
-static void add_interrupt_bench(cycles_t start)
-{
-	long delta = random_get_entropy() - start;
-
-	/* Use a weighted moving average */
-	delta = delta - ((avg_cycles + FIXED_1_2) >> AVG_SHIFT);
-	avg_cycles += delta;
-	/* And average deviation */
-	delta = abs(delta) - ((avg_deviation + FIXED_1_2) >> AVG_SHIFT);
-	avg_deviation += delta;
-}
-#else
-#define add_interrupt_bench(x)
-#endif
-
 static u32 get_reg(struct fast_pool *f, struct pt_regs *regs)
 {
 	u32 *ptr = (u32 *)regs;
@@ -865,7 +842,6 @@ void add_interrupt_randomness(int irq)
 		(sizeof(ip) > 4) ? ip >> 32 : get_reg(fast_pool, regs);
 
 	fast_mix(fast_pool);
-	add_interrupt_bench(cycles);
 
 	if (unlikely(crng_init == 0)) {
 		if (fast_pool->count >= 64 &&
@@ -1574,22 +1550,6 @@ static struct ctl_table random_table[] = {
 		.mode		= 0444,
 		.proc_handler	= proc_do_uuid,
 	},
-#ifdef ADD_INTERRUPT_BENCH
-	{
-		.procname	= "add_interrupt_avg_cycles",
-		.data		= &avg_cycles,
-		.maxlen		= sizeof(avg_cycles),
-		.mode		= 0444,
-		.proc_handler	= proc_doulongvec_minmax,
-	},
-	{
-		.procname	= "add_interrupt_avg_deviation",
-		.data		= &avg_deviation,
-		.maxlen		= sizeof(avg_deviation),
-		.mode		= 0444,
-		.proc_handler	= proc_doulongvec_minmax,
-	},
-#endif
 	{ }
 };