Re: [dpdk-dev] Use WFE for spinlock and ring

[Ruifeng Wang <Ruifeng.Wang@arm.com>]

> -----Original Message-----
> From: Stephen Hemminger <stephen@networkplumber.org>
> Sent: Wednesday, July 7, 2021 10:48 PM
> To: Ruifeng Wang <Ruifeng.Wang@arm.com>
> Cc: dev@dpdk.org; david.marchand@redhat.com; thomas@monjalon.net;
> jerinj@marvell.com; nd <nd@arm.com>; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>
> Subject: Re: [dpdk-dev] Use WFE for spinlock and ring
> 
> On Sun, 25 Apr 2021 05:56:51 +0000
> Ruifeng Wang <ruifeng.wang@arm.com> wrote:
> 
> > The rte_wait_until_equal_xxx APIs abstract the functionality of
> > 'polling for a memory location to become equal to a given value'[1].
> >
> > Use the API for the rte spinlock and ring implementations.
> > With the wait until equal APIs being stable, changes will not impact ABI.
> >
> > [1] http://patches.dpdk.org/cover/62703/
> >
> > v3:
> > Series rebased. (David)
> >
> > Gavin Hu (1):
> >   spinlock: use wfe to reduce contention on aarch64
> >
> > Ruifeng Wang (1):
> >   ring: use wfe to wait for ring tail update on aarch64
> >
> >  lib/eal/include/generic/rte_spinlock.h | 4 ++--
> >  lib/ring/rte_ring_c11_pvt.h            | 4 ++--
> >  lib/ring/rte_ring_generic_pvt.h        | 3 +--
> >  3 files changed, 5 insertions(+), 6 deletions(-)
> >
> 
> Other places that should use WFE:
Thank you Stephen for looking into this.

> 
> rte_mcslock.h:rte_mcslock_lock()
Existing API can be used in this one.

> rte_mcslock_unlock:rte_mcslock_unlock()
This one needs rte_wait_while_xxx variant.

> 
> rte_pflock.h:rte_pflock_lock()
> rte_rwlock.h:rte_rwlock_read_lock()
> rte_rwlock.h:rte_rwlock_write_lock()
These occurrences have extra logic (AND, conditional branch, CAS) in the loop.
I'm not sure generic API can be abstracted from these use cases.

> 
> 
> You should also introduce rte_wait_while_XXX variants to handle some of
> these cases.
>