svn commit: r229085 - in head/sys: amd64/amd64 i386/i386

Gavin Atkinson gavin at FreeBSD.org
Sat Dec 31 13:24:54 UTC 2011


Author: gavin
Date: Sat Dec 31 13:24:53 2011
New Revision: 229085
URL: http://svn.freebsd.org/changeset/base/229085

Log:
  Default to not performing the early-boot memory tests when we detect we
  are booting inside a VM.  There are three reasons to disable this:
  
  o  It causes the VM host to believe that all the tested pages or RAM are
     in use.  This in turn may force the host to page out pages of RAM
     belonging to other VMs, or otherwise cause problems with fair resource
     sharing on the VM cluster.
  o  It adds significant time to the boot process (around 1 second/Gig in
     testing)
  o  It is unnecessary - the host should have already verified that the
     memory is functional etc.
  
  Note that this simply changes the default when in a VM - it can still be
  overridden using the hw.memtest.tests tunable.
  
  MFC after:	4 weeks

Modified:
  head/sys/amd64/amd64/machdep.c
  head/sys/i386/i386/machdep.c

Modified: head/sys/amd64/amd64/machdep.c
==============================================================================
--- head/sys/amd64/amd64/machdep.c	Sat Dec 31 13:23:04 2011	(r229084)
+++ head/sys/amd64/amd64/machdep.c	Sat Dec 31 13:24:53 2011	(r229085)
@@ -1401,10 +1401,13 @@ getmemsize(caddr_t kmdp, u_int64_t first
 		Maxmem = atop(physmem_tunable);
 
 	/*
-	 * By default keep the memtest enabled.  Use a general name so that
+	 * By default enable the memory test on real hardware, and disable
+	 * it if we appear to be running in a VM.  This avoids touching all
+	 * pages unnecessarily, which doesn't matter on real hardware but is
+	 * bad for shared VM hosts.  Use a general name so that
 	 * one could eventually do more with the code than just disable it.
 	 */
-	memtest = 1;
+	memtest = (vm_guest > VM_GUEST_NO) ? 0 : 1;
 	TUNABLE_ULONG_FETCH("hw.memtest.tests", &memtest);
 
 	/*

Modified: head/sys/i386/i386/machdep.c
==============================================================================
--- head/sys/i386/i386/machdep.c	Sat Dec 31 13:23:04 2011	(r229084)
+++ head/sys/i386/i386/machdep.c	Sat Dec 31 13:24:53 2011	(r229085)
@@ -2369,10 +2369,13 @@ physmap_done:
 		Maxmem = atop(physmap[physmap_idx + 1]);
 
 	/*
-	 * By default keep the memtest enabled.  Use a general name so that
+	 * By default enable the memory test on real hardware, and disable
+	 * it if we appear to be running in a VM.  This avoids touching all
+	 * pages unnecessarily, which doesn't matter on real hardware but is
+	 * bad for shared VM hosts.  Use a general name so that
 	 * one could eventually do more with the code than just disable it.
 	 */
-	memtest = 1;
+	memtest = (vm_guest > VM_GUEST_NO) ? 0 : 1;
 	TUNABLE_ULONG_FETCH("hw.memtest.tests", &memtest);
 
 	if (atop(physmap[physmap_idx + 1]) != Maxmem &&


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