(+ Steve)
Hello Saurabh, On 11/18/2024 3:09 PM, Saurabh Sengar wrote:
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.
Steve too was optimizing this path. I believe his latest version can be found at: https://lore.kernel.org/lkml/20241031200431.182443-1-steve.wahl@hpe.com/
Does that approach help improving bootup time for you? Valentine suggested the same approach as yours on a previous version of Steve's optimization but Steve believed returning true can possibly have other implication in the sched-domain building path. The thread can be found at: https://lore.kernel.org/lkml/Zw_k_WFeYFli87ck@swahl-home.5wahls.com/
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 wants 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
[V2]
- Use kernel cmdline param instead of compile time flag.
kernel/sched/topology.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index 9748a4c8d668..4ca63bff321d 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -2363,6 +2363,13 @@ 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_verbose) {
nit.
I think the convention in topology.c is to call "sched_debug()" and not check "sched_debug_verbose" directly.
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;