svn commit: r327651 - stable/11/sys/amd64/vmm/io

[Ian Lepore]

Author: ian
Date: Sat Jan  6 22:56:48 2018
New Revision: 327651
URL: https://svnweb.freebsd.org/changeset/base/327651

Log:
  MFC r325108:
  
  Improve the performance of the hpet timer in bhyve guests by making the
  timer frequency a power of two.  This changes the frequency from 10 to
  16.7 MHz (2 ^ 24 HZ).  Using a power of two avoids roundoff errors when
  doing arithmetic in sbintime_t units.
  
  Testing shows this can fix erratic ntpd behavior in guests using the
  hpet timer (which is the default for multicore guests).

Modified:
  stable/11/sys/amd64/vmm/io/vhpet.c
Directory Properties:
  stable/11/   (props changed)

Modified: stable/11/sys/amd64/vmm/io/vhpet.c
==============================================================================
--- stable/11/sys/amd64/vmm/io/vhpet.c	Sat Jan  6 21:37:23 2018	(r327650)
+++ stable/11/sys/amd64/vmm/io/vhpet.c	Sat Jan  6 22:56:48 2018	(r327651)
@@ -51,7 +51,7 @@ __FBSDID("$FreeBSD$");
 
 static MALLOC_DEFINE(M_VHPET, "vhpet", "bhyve virtual hpet");
 
-#define	HPET_FREQ	10000000		/* 10.0 Mhz */
+#define	HPET_FREQ	16777216		/* 16.7 (2^24) Mhz */
 #define	FS_PER_S	1000000000000000ul
 
 /* Timer N Configuration and Capabilities Register */