From: Saurabh Sengar ssengar@linux.microsoft.com
On a x86 system under test with 1780 CPUs, topology_span_sane() takes around 8 seconds cumulatively for all the iterations. It is an expensive operation which does the sanity of non-NUMA topology masks.
CPU topology is not something which changes very frequently hence make this check optional for the systems where the topology is trusted and need faster bootup.
Restrict this to sched_verbose kernel cmdline option so that this penalty can be avoided for the systems who want to avoid it.
Cc: stable@vger.kernel.org Fixes: ccf74128d66c ("sched/topology: Assert non-NUMA topology masks don't (partially) overlap") Signed-off-by: Saurabh Sengar ssengar@linux.microsoft.com Co-developed-by: Naman Jain namjain@linux.microsoft.com Signed-off-by: Naman Jain namjain@linux.microsoft.com ---
Changes since v2: https://lore.kernel.org/all/1731922777-7121-1-git-send-email-ssengar@linux.m... - Use sched_debug() instead of using sched_debug_verbose variable directly (addressing Prateek's comment)
Changes since v1: https://lore.kernel.org/all/1729619853-2597-1-git-send-email-ssengar@linux.m... - Use kernel cmdline param instead of compile time flag.
Adding a link to the other patch which is under review. https://lore.kernel.org/lkml/20241031200431.182443-1-steve.wahl@hpe.com/ Above patch tries to optimize the topology sanity check, whereas this patch makes it optional. We believe both patches can coexist, as even with optimization, there will still be some performance overhead for this check.
--- kernel/sched/topology.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index c49aea8c1025..b030c1a2121f 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -2359,6 +2359,13 @@ static bool topology_span_sane(struct sched_domain_topology_level *tl, { int i = cpu + 1;
+ /* Skip the topology sanity check for non-debug, as it is a time-consuming operatin */ + if (!sched_debug()) { + pr_info_once("%s: Skipping topology span sanity check. Use `sched_verbose` boot parameter to enable it.\n", + __func__); + return true; + } + /* NUMA levels are allowed to overlap */ if (tl->flags & SDTL_OVERLAP) return true;
base-commit: 00f3246adeeacbda0bd0b303604e46eb59c32e6e