Re: [dpdk-dev] [EXT] [PATCH v3 6/6] spinlock: ticket based to improve fairness

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 27 Dec 2018 12:08:26 +0000
Jerin Jacob Kollanukkaran <jerinj@marvell.com> wrote:

> On Thu, 2018-12-27 at 10:05 +0000, Gavin Hu (Arm Technology China)
> wrote:
> > > -----Original Message-----
> > > From: Jerin Jacob Kollanukkaran <jerinj@marvell.com>
> > > Sent: Thursday, December 27, 2018 2:58 PM
> > > To: Gavin Hu (Arm Technology China) <Gavin.Hu@arm.com>; 
> > > dev@dpdk.org
> > > Cc: david.marchand@redhat.com; chaozhu@linux.vnet.ibm.com; nd
> > > <nd@arm.com>; bruce.richardson@intel.com; thomas@monjalon.net;
> > > Joyce
> > > Kong (Arm Technology China) <Joyce.Kong@arm.com>;
> > > hemant.agrawal@nxp.com; stephen@networkplumber.org; Honnappa
> > > Nagarahalli <Honnappa.Nagarahalli@arm.com>
> > > Subject: Re: [EXT] [PATCH v3 6/6] spinlock: ticket based to improve
> > > fairness
> > > 
> > > On Thu, 2018-12-27 at 12:13 +0800, Gavin Hu wrote:  
> > > > ---------------------------------------------------------------
> > > > ----
> > > > ---
> > > > From: Joyce Kong <joyce.kong@arm.com>
> > > > 
> > > > The old implementation is unfair, some threads may take locks
> > > > aggressively  
> > > 
> > > I think, one issue here is x86 and ppc follows traditional spinlock
> > > and
> > > arm64 will be following ticket lock for spinlock implementation.
> > > This would change application behaviour on arm64 compared to x86
> > > and
> > > ppc.
> > > 
> > > How about having a separate API for ticket lock? That would give,
> > > # application choice to use the locking strategy
> > > # application behaviour will be same across all arch.  
> > 
> > Ok, will do in v4 to have a new named rte_ticket_spinlock API.  
> 
> I would prefer rte_ticketlock_[lock/unlock/trylock/is_locked] name
> instead of rte_ticket_spinlock_lock etc to reduce the length of the
> API.


NAK to adding new API for this.

I want the best possible locks for all applications and all architectures.
These should be called spinlock so there is no requirement for application
to change to get better performance. Why not just implement the best algorithm
across the board. Yes, this means collaboration or working on the other guys
architecture.