On Thu, Mar 5, 2026 at 5:44 AM David Laight <[email protected]> wrote: > > On Wed, 4 Mar 2026 15:57:42 -0500 > Steven Rostedt <[email protected]> wrote: > > > On Wed, 4 Mar 2026 09:54:15 +0000 > > David Laight <[email protected]> wrote: > > > > > That might still be an issue if a high priority process is spinning. > > > But a %sys spike doesn't imply a latency spike. > > > > > > Is this using the osq_lock.c code? > > > That will have problems on overprovisioned VMs, it tries to find out > > > whether the hypervisor has switched out - but ISTR that is flawed. > > > > > > In reality a spin lock shouldn't be held for long enough to cause > > > any kind latency issue. > > > So something in the code that reads the list of filter functions > > > needs to be done differently so that the lock isn't held for as long. > > > > It's not a spinlock, it's an adaptive mutex which spins while the owner of > > the mutex is also still running on the CPU. If the spinner CPU triggers a > > NEED_RESCHED or the owner goes to sleep, the spinner stops spinning and > > goes to sleep too. > > I think half my brain knew that - otherwise I wouldn't have mentioned > the osq_lock.c code. > That all reminded me I've a patch that optimises that code a bit. > But I do remember thinking it ought to have a 'I been spinning long > enough, time to sleep' path. > > David > > > > > Honestly, this still looks like a non-issue or a corner case that I don't > > think requires these changes. > > > > This looks like one of those "Patient: Doctor it hurts me when I do this. > > Doctor: Then don't do that." cases. > > > > Why is a production system having multiple users cat > > avaliable_filter_functions to begin with?
bpftrace is a widely used tool for online debugging and dynamic tracing. However, sysadmins may unknowingly run multiple bpftrace instances concurrently without realizing the potential impact on system performance. If this is your answer, I believe we should clearly document the following warning: Warning: Do not read available_filter_functions concurrently, as doing so can significantly degrade system performance and potentially impact production workloads. -- Regards Yafang
