[Xen-devel] [OSSTEST PATCH 6/6] builds: Run i386 builds on amd64 kernels

[Ian Jackson <ian.jackson@xxxxxxxxxxxxx>]

Most hardware that supports i386 supports amd64 too.  When doing
builds we do need the right userland, but we don't actually care what
the kernel is doing.  With Linux 32-on-64 is good for that.

Especially, there is a kernel regression (evident in the Debian
stretch kernel, but not present in jessie's) where 32-bit Linux
mismanages the memory on hosts with moderately large amounts of
RAM (ie, significantly more RAM than can be addressed at once),
resulting in what amounts to a near-stall of the paging system.  Since
the paging system is used for filesystem writes too, the effect is
that commands run by builds can take totally unreasonable amounts of
time.  Ie, this version of Linux is broken when i386 PAE is needed.

In practice this is causing significant trouble in the Xen Project CI.

This kernel bug probably won't affect our test jobs because
(i) we use our own kernels, so we would probably detect this
regression when switching kernel branches etc. (ii) test jobs
run with a dom0_mem setting which avoids the preconditions for the
particular bug.

CC: Juergen Gross <jgross@xxxxxxxx>
CC: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Paul Durrant <paul.durrant@xxxxxxxxxx>
Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---
 ts-host-install | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/ts-host-install b/ts-host-install
index 7094559f..45f04764 100755
--- a/ts-host-install
+++ b/ts-host-install
@@ -31,6 +31,7 @@ my $debconf_priority;
 my $poweron_test_only;
 
 our %xopts;
+our $kern_arch_info;
 
 while (@ARGV and $ARGV[0] =~ m/^-/) {
     $_= shift @ARGV;
@@ -42,6 +43,12 @@ while (@ARGV and $ARGV[0] =~ m/^-/) {
     } elsif  (m/^--rescue$/) {
        $xopts{RescueMode}= 1;
     } elsif  (m/^--build$/) {
+       if ($r{arch} eq 'i386') {
+           $kern_arch_info = {
+                Kernel_Debian => 'amd64',
+                Userland_setarch => 'i386',
+            };
+       }
     } else {
        die "$_ $!";
     }
@@ -61,6 +68,7 @@ sub install () {
         ($ho, '',
          DiskDevice => $ho->{DiskDevice},
          Properties => $ho->{Properties},
+        LinuxKernPreferredArchInfo => $kern_arch_info,
          ExtraPreseed => <<END );
 d-i netcfg/get_hostname string $ho->{Name}
 d-i netcfg/get_ipaddress string $ho->{Ip}
-- 
2.11.0


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