From: Jonathan McDowell <noodles-github@earth.li>
Date: Fri, 23 Mar 2018 00:35:52 +0000 (+0000)
Subject: Allow use of ARM64 CNTVCT_EL0 register for timing (#46)
X-Git-Tag: 3.0.0-245~73
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=fc465074c99962dbbb2d9716709963831de689f1;p=thirdparty%2Fsnort3.git

Allow use of ARM64 CNTVCT_EL0 register for timing (#46)

snort supports the use of rdtsc to get fast, accurate-enough timing on
x86 platforms. The CNTVCT_EL0 register on ARM64 provides a usable
equivalent to userspace code on that platform. It's not the actual
processor clock rate but can vary in accuracy from 1-50Mhz. Its use
gives a ~10% performance improvement on an A53 based platform.
---

diff --git a/src/time/tsc_clock.h b/src/time/tsc_clock.h
index 68dd81b53..c7729808a 100644
--- a/src/time/tsc_clock.h
+++ b/src/time/tsc_clock.h
@@ -48,9 +48,17 @@ struct TscClock
 
     static uint64_t counter()
     {
+#if defined(__aarch64__)
+        uint64_t ticks;
+
+        asm volatile("mrs %0, CNTVCT_EL0" : "=r" (ticks));
+        return ticks;
+#else
+        // Default to x86, other archs will compile error anyway
         uint32_t lo, hi;
         asm volatile("rdtsc" : "=a" (lo), "=d" (hi));
         return ((uint64_t)hi << 32) | lo;
+#endif
     }
 
     static time_point now() noexcept