On 28.04.21 11:25, Peter Zijlstra wrote:
On Wed, Apr 28, 2021 at 10:54:37AM +0200, Christian Borntraeger wrote:
On 28.04.21 10:46, Peter Zijlstra wrote:
On Tue, Apr 27, 2021 at 04:59:25PM +0200, Christian Borntraeger wrote:
Peter,
I just realized that we moved away sysctl tunabled to debugfs in next.
We have seen several cases where it was benefitial to set
sched_migration_cost_ns to a lower value. For example with KVM I can
easily get 50% more transactions with 50000 instead of 500000.
Until now it was possible to use tuned or /etc/sysctl.conf to set
these things permanently.
Given that some people do not want to have debugfs mounted all the time
I would consider this a regression. The sysctl tunable was always
available.
I am ok with the "informational" things being in debugfs, but not
the tunables. So how do we proceed here?
It's all SCHED_DEBUG; IOW you're relying on DEBUG infrastructure for
production performance, and that's your fail.
No its not. sched_migration_cost_ns was NEVER protected by CONFIG_SCHED_DEBUG.
It was available on all kernels with CONFIG_SMP.
The relevant section from origin/master:kernel/sysctl.c:
[...]
How is migration_cost not under SCHED_DEBUG? The bigger problem is that
world+dog has SCHED_DEBUG=y in their .config.
Hmm, yes my bad. I disabled it but it was silently reenabled due to a
dependency. So yes you are right, it is under SCHED_DEBUG.
