Re: [RFC v4 3/4] irqflags: Avoid unnecessary calls to trace_ if you can

From: Joel Fernandes
Date: Tue Apr 24 2018 - 15:01:25 EST

On Tue, Apr 24, 2018 at 11:59 AM, Joel Fernandes <joelaf@xxxxxxxxxx> wrote:
>>> > > By the way is there any limitation on using SRCU too early during
>>> > > boot? I backported Mathieu's srcu tracepoint patches but the kernel
>>> > > hangs pretty early in the boot. I register lockdep probes in
>>> > > start_kernel. I am hoping that's not why.
>>> > >
>>> > > I could also have just screwed up the backporting... may be for my
>>> > > testing, I will just replace the rcu API with the srcu instead of all
>>> > > of Mathieu's new TRACE_EVENT macros for SRCU, since all I am trying to
>>> > > do right now is measure the performance of my patches with SRCU.
>>> >
>>> > Gah, yes, there is an entry on my capacious todo list on making SRCU
>>> > grace periods work during early boot and mid-boot. Let me see what
>>> > I can do...
>>> OK, just need to verify that you are OK with call_srcu()'s callbacks
>>> not being invoked until sometime during core_initcall() time. (If you
>>> really do need them to be invoked before that, in theory it is possible,
>>> but in practice it is weird, even for RCU.)
>> Oh, and that early at boot, you will need to use DEFINE_SRCU() or
>> DEFINE_STATIC_SRCU() rather than dynamic allocation and initialization.
>> Thanx, Paul
> Oh ok.
> About call_rcu, calling it later may be an issue since we register the
> probes in start_kernel, for the first probe call_rcu will be sched,

Sorry, I need to start proof reading my emails. s/sched/skipped/


- Joel