[dpdk-dev] [PATCH v5 1/3] rcu: add RCU library supporting QSBR mechanism

[Stephen Hemminger]

On Mon, 15 Apr 2019 12:24:47 +0000
"Ananyev, Konstantin" <konstantin.ananyev at intel.com> wrote:

> > -----Original Message-----
> > From: Stephen Hemminger [mailto:stephen at networkplumber.org]
> > Sent: Saturday, April 13, 2019 12:06 AM
> > To: Honnappa Nagarahalli <Honnappa.Nagarahalli at arm.com>
> > Cc: Ananyev, Konstantin <konstantin.ananyev at intel.com>; paulmck at linux.ibm.com; Kovacevic, Marko <marko.kovacevic at intel.com>;
> > dev at dpdk.org; Gavin Hu (Arm Technology China) <Gavin.Hu at arm.com>; Dharmik Thakkar <Dharmik.Thakkar at arm.com>; Malvika Gupta
> > <Malvika.Gupta at arm.com>; nd <nd at arm.com>
> > Subject: Re: [PATCH v5 1/3] rcu: add RCU library supporting QSBR mechanism
> > 
> > On Fri, 12 Apr 2019 22:24:45 +0000
> > Honnappa Nagarahalli <Honnappa.Nagarahalli at arm.com> wrote:
> >   
> > > >
> > > > On Fri, 12 Apr 2019 15:20:37 -0500
> > > > Honnappa Nagarahalli <honnappa.nagarahalli at arm.com> wrote:
> > > >  
> > > > > Add RCU library supporting quiescent state based memory reclamation  
> > > > method.  
> > > > > This library helps identify the quiescent state of the reader threads
> > > > > so that the writers can free the memory associated with the lock less
> > > > > data structures.
> > > > >
> > > > > Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>
> > > > > Reviewed-by: Steve Capper <steve.capper at arm.com>
> > > > > Reviewed-by: Gavin Hu <gavin.hu at arm.com>
> > > > > Reviewed-by: Ola Liljedahl <ola.liljedahl at arm.com>
> > > > > Acked-by: Konstantin Ananyev <konstantin.ananyev at intel.com>  
> > > >
> > > > After evaluating long term API/ABI issues, I think you need to get rid of almost
> > > > all use of inline and visible structures. Yes it might be marginally slower, but
> > > > you thank me the first time you have to fix something.
> > > >  
> > > Agree, I was planning on another version to address this (I am yet to take a look at your patch addressing the ABI).
> > > The structure visibility definitely needs to be addressed.
> > > For the inline functions, is the plan to convert all the inline functions in DPDK? If yes, I think we need to consider the performance  
> > difference. May be consider L3-fwd application, change all the inline functions in its path and run a test?
> > 
> > Every function that is not in the direct datapath should not be inline.
> > Exceptions or things like rx/tx burst, ring enqueue/dequeue, and packet alloc/free  
> 
> Plus synchronization routines: spin/rwlock/barrier, etc.
> I think rcu should be one of such exceptions - it is just another synchronization mechanism after all
> (just a bit more sophisticated).
> Konstantin

If you look at the other userspace RCU, you wil see that the only inlines
are the rcu_read_lock,rcu_read_unlock and rcu_reference/rcu_assign_pointer.

The synchronization logic is all real functions.