Re: [TAPSETS] Linux Kernel Event Trace Tool

["Guanglei Li" <guanglei at cn dot ibm dot com>]

> > So how about using semaphore in probe handler or spin lock in
> > _stp_sprintf. So that no event will be lost.
>
> Whom would such a spinlock protect against?  There is intended to be
> no locking that synchronizes separate CPUs running probes, except 
> when
> these scripts access shared ("global"-declared) systemtap variables.
> - FChE

protect against _stp_pbuf[cpu] & _stp_pbuf_len[cpu]. But as you 
mentioned, it may not be so easy for systemtap.


> > The current implementation will just abandon the processing of a
> > probe handler if there's already another probe handler running, 
> > even
> > on a different CPU.
>
> Why do you think so?  Reentrancy is assessed on a per-cpu basis.
> Concurrency across CPUs is not explicitly blocked, except as above.
> - FChE
sorry, I missed the following statement:
struct context* c = per_cpu_ptr (contexts, smp_processor_id());
so the context is a per cpu variable.