(+ 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@xxxxxxx/
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@xxxxxxxxxxxxxxxxxxxxx/
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@xxxxxxxxxxxxxxx
Fixes: ccf74128d66c ("sched/topology: Assert non-NUMA topology masks don't (partially) overlap")
Signed-off-by: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx>
---
[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;
--
Thanks and Regards,
Prateek
