Messages in this thread | | | Subject | Re: divide error in select_task_rq_fair() | From | Myron Stowe <> | Date | Sun, 14 Nov 2010 10:36:01 -0700 |
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On Fri, 2010-11-12 at 11:52 +0530, Nikanth Karthikesan wrote: > On Thursday 11 November 2010 23:58:04 Myron Stowe wrote: > > On Fri, 2010-11-05 at 07:17 +0100, Eric Dumazet wrote: > > > Le jeudi 04 novembre 2010 à 20:00 -0600, Bjorn Helgaas a écrit : > > > > Is that going to help you debug the problem? The solution is not going > > > > to be something like "set NR_CPUS=x". If NR_CPUS is too small, the > > > > machine should still *boot*, even if we can't use all the CPUs in the > > > > box. > > > > > > Yes, it will help to understand the layout of cpu / domains and make > > > appropriate changes. > > > > > > Alternative is you send me such a machine :=) > > > > I opened a BZ on this issue as it seems to be a regression - > > https://bugzilla.kernel.org/show_bug.cgi?id=22662 > > > > I also, as indicated in the BZ, bisected the kernel which gave the > > following results and reverting 50f2d7f682f9c0ed58191d0982fe77888d59d162 > > did re-enable booting on the box in question (an HP dl980g7). Let me > > know what further info you need or patches to test for debugging this. > > > > Thanks, > > > > commit 50f2d7f682f9c0ed58191d0982fe77888d59d162 > > Author: Nikanth Karthikesan <knikanth@suse.de> > > Date: Thu Sep 30 17:34:10 2010 +0530 > > > > x86, numa: Assign CPUs to nodes in round-robin manner on fake NUMA > > > > commit d9c2d5ac6af87b4491bff107113aaf16f6c2b2d9 "x86, numa: Use > > near(er) online node instead of roundrobin for NUMA" changed NUMA > > initialization on Intel to choose the nearest online node or first node. > > Fake NUMA would be better of with round-robin initialization, instead of > > the all CPUS on first node. Change the choice of first node, back to > > round-robin. > > > > For testing NUMA kernel behaviour without cpusets and NUMA aware > > applications, it would be better to have cpus in different nodes, > > rather than all in a single node. With cpusets migration of tasks > > scenarios cannot not be tested. > > > > I guess having it round-robin shouldn't affect the use cases for all > > cpus on the first node. > > > > The code comments in arch/x86/mm/numa_64.c:759 indicate that this used > > to be the case, which was changed by commit d9c2d5ac6. It changed from > > roundrobin to nearer or first node. And I couldn't find any reason for > > this change in its changelog. > > > > Signed-off-by: Nikanth Karthikesan <knikanth@suse.de> > > Cc: David Rientjes <rientjes@google.com> > > Signed-off-by: Andrew Morton <akpm@linux-foundation.org> > > > > > Thanks > > > > Can you try with this patch?
I got the same divide error with this latest patch (see attachment). If I revert commit 50f2d7f682f9, the platform boots successfully.
Thanks,
Myron
> > Thanks > Nikanth > > Fallback to first node, if the node is not online. > > Fixes regression of commit 50f2d7f682f9c0ed58191d0982fe77888d59d162 > x86, numa: Assign CPUs to nodes in round-robin manner on fake NUMA > > When some of the NUMA nodes are disabled, and the CPUs are assigned > in round-robin fashion, CPUs might be assigned to disabled nodes > resulting in the crash. While using round-robin assignment, check if the > node is online. If the node is not online, use the first online node. > > Reported-by: Bjorn Helgaas <bjorn.helgaas@hp.com> > Signed-off-by: Nikanth Karthikesan <knikanth@suse.de> > > --- > > diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c > index d16c2c5..f31237c 100644 > --- a/arch/x86/kernel/cpu/intel.c > +++ b/arch/x86/kernel/cpu/intel.c > @@ -287,6 +287,8 @@ static void __cpuinit srat_detect_node(struct cpuinfo_x86 *c) > if (node == NUMA_NO_NODE || !node_online(node)) { > /* reuse the value from init_cpu_to_node() */ > node = cpu_to_node(cpu); > + if (!node_online(node)) > + node = first_node(node_online_map); > } > numa_set_node(cpu, node); > #endif >
-- Myron Stowe Linux Kernel Developer Fort Collins, CO Office of Corporate Strategy and Technology
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