Re: [dpdk-dev] [RFC PATCH v3 4/5] lib/bpf: use wait event scheme for Rx/Tx iteration

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> -----Original Message-----
> From: Ananyev, Konstantin
> Sent: Thursday, October 7, 2021 4:50 PM
> To: Feifei Wang <feifei.wang2@arm.com>
> Cc: dev@dpdk.org; nd@arm.com; Ruifeng Wang <ruifeng.wang@arm.com>
> Subject: RE: [RFC PATCH v3 4/5] lib/bpf: use wait event scheme for Rx/Tx iteration
> 
> 
> 
> >
> > Signed-off-by: Feifei Wang <feifei.wang2@arm.com>
> > Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> > ---
> >  lib/bpf/bpf_pkt.c | 9 +++------
> >  1 file changed, 3 insertions(+), 6 deletions(-)
> >
> > diff --git a/lib/bpf/bpf_pkt.c b/lib/bpf/bpf_pkt.c
> > index 6e8248f0d6..3af15ae97b 100644
> > --- a/lib/bpf/bpf_pkt.c
> > +++ b/lib/bpf/bpf_pkt.c
> > @@ -113,7 +113,7 @@ bpf_eth_cbi_unuse(struct bpf_eth_cbi *cbi)
> >  static void
> >  bpf_eth_cbi_wait(const struct bpf_eth_cbi *cbi)
> >  {
> > -	uint32_t nuse, puse;
> > +	uint32_t puse;
> >
> >  	/* make sure all previous loads and stores are completed */
> >  	rte_smp_mb();
> > @@ -122,11 +122,8 @@ bpf_eth_cbi_wait(const struct bpf_eth_cbi *cbi)
> >
> >  	/* in use, busy wait till current RX/TX iteration is finished */
> >  	if ((puse & BPF_ETH_CBI_INUSE) != 0) {
> > -		do {
> > -			rte_pause();
> > -			rte_compiler_barrier();
> > -			nuse = cbi->use;
> > -		} while (nuse == puse);
> > +		rte_compiler_barrier();
> > +		rte_wait_event_32(&cbi->use, UINT_MAX, puse, ==, __ATOMIC_RELAXED);

Probably UINT32_MAX will be a bit better here.

> 
> If we do use atomic load, while we still need a compiler_barrier() here?
> 
> >  	}
> >  }
> >
> > --
> > 2.25.1