On 2015/1/29 4:47, Jason Low wrote:
> The cpuset.sched_relax_domain_level can control how far we do
> immediate load balancing on a system. However, it was found on recent
> kernels that echo'ing a value into cpuset.sched_relax_domain_level
> did not reduce any immediate load balancing.
>
> The reason this occurred was because the update_domain_attr_tree() traversal
> did not update for the "top_cpuset". This resulted in nothing being changed
> when modifying the sched_relax_domain_level parameter.
>
> This patch was able to address that problem by having update_domain_attr_tree()
> allowing updates for the root (top_cpuset) in the cpuset traversal.
>
> Signed-off-by: Jason Low <jason.low2@xxxxxx>
Thanks for finding this bug!
Please Add:
Cc: <stable@xxxxxxxxxxxxxxx> # 3.9+
Fixes: fc560a26acce ("cpuset: replace cpuset->stack_list with cpuset_for_each_descendant_pre()")
I'll prepare a different fix for 3.10.y when this patch hits mainline.
> ---
> kernel/cpuset.c | 12 +++++++-----
> 1 files changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> index 64b257f..0f58c54 100644
> --- a/kernel/cpuset.c
> +++ b/kernel/cpuset.c
> @@ -541,15 +541,17 @@ update_domain_attr(struct sched_domain_attr *dattr, struct cpuset *c)
> }
>
> static void update_domain_attr_tree(struct sched_domain_attr *dattr,
> - struct cpuset *root_cs)
> + struct cpuset *root_cs, bool update_root)
> {
> struct cpuset *cp;
> struct cgroup_subsys_state *pos_css;
>
> rcu_read_lock();
> cpuset_for_each_descendant_pre(cp, pos_css, root_cs) {
> - if (cp == root_cs)
> - continue;
I don't think this fix is correct. We should simply remove these two lines,
and no other changes are needed.
> + if (cp == root_cs) {
> + if (!update_root)
> + continue;
> + }
>
> /* skip the whole subtree if @cp doesn't have any CPU */
> if (cpumask_empty(cp->cpus_allowed)) {
> @@ -644,7 +646,7 @@ static int generate_sched_domains(cpumask_var_t **domains,
> dattr = kmalloc(sizeof(struct sched_domain_attr), GFP_KERNEL);
> if (dattr) {
> *dattr = SD_ATTR_INIT;
> - update_domain_attr_tree(dattr, &top_cpuset);
> + update_domain_attr_tree(dattr, &top_cpuset, true);
> }
> cpumask_copy(doms[0], top_cpuset.effective_cpus);
>
> @@ -752,7 +754,7 @@ restart:
> if (apn == b->pn) {
> cpumask_or(dp, dp, b->effective_cpus);
> if (dattr)
> - update_domain_attr_tree(dattr + nslot, b);
> + update_domain_attr_tree(dattr + nslot, b, false);
>
> /* Done with this partition */
> b->pn = -1;
>
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