On Wed, 22 Jan 2020 16:23:17 +0900 Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote: > On Tue, 21 Jan 2020 19:29:05 -0500 > Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > > On Thu, 16 Jan 2020 23:44:52 +0900 > > Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote: > > > > > Since the 5 jiffies delay for the optimizer is too > > > short to wait for other probes, make it longer, > > > like 1 second. > > > > Hi Masami, > > > > Can you explain more *why* 5 jiffies is too short. > > Yes, I had introduced this 5 jiffies delay for multiple probe registration > and unregistration like systemtap, which will use array-based interface to > register/unregister. In that case, 5 jiffies will be enough for the delay > to wait for other kprobe registration/unregsitration. > > However, since perf and ftrace register/unregister probes one-by-one with > RCU synchronization interval, the optimizer will be started before > finishing to register/unregister all probes. > And the optimizer locks kprobe_mutex a while -- RCU-tasks synchronization. > Since the kprobe_mutex is also involved in disabling kprobes, this also > stops probe-event disabling. > > Maybe 5 jiffies is enough for adding/removing a few probe events, but > not enough for dozens of probe events. > Perhaps we should have a mechanism that can detect new probes being added, and just continue to delay the optimization, instead of having some arbitrary delay. -- Steve
