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Message-ID: <20140614080329.29871.qmail@ns.horizon.com>
Date: 14 Jun 2014 04:03:29 -0400
From: "George Spelvin" <linux@...izon.com>
To: linux@...izon.com, tytso@....edu
Cc: hpa@...ux.intel.com, linux-kernel@...r.kernel.org,
mingo@...nel.org, price@....edu
Subject: Re: random: Benchamrking fast_mix2
> Want to give this patch a try on your collection of machines?
Not until I fix it to
+#if ADD_INTERRUPT_BENCH
+static unsigned long avg_cycles;
+
+#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)
+{
+ cycles_t duration = random_get_entropy() - start;
+
+ /* Use a weighted moving average */
+ avg_cycles += ((avg_cycles + FIXED_1_2) >> AVG_SHIFT) - duration;
+}
+#else
+#define add_interrupt_bench(x)
+#endif
+
... because the way you did it was just silly.
See net/ipv4/tcp_input.c:tcp_rtt_estimator().
That also shows you how to add a mean deviation estimator, too.
I'll go do that now...
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