> Hi Feifei,
>
> > > Instead of polling for cbi->use to be updated, use wait event scheme.
> > >
> > > Furthermore, delete 'const' for 'bpf_eth_cbi_wait'. This is because of a
> > > compilation error:
> > > -----------------------------------------------------------------------
> > > ../lib/eal/include/rte_common.h:36:13: error: read-only variable ‘value’
> > > used as ‘asm’ output
> > > 36 | #define asm __asm__
> > > | ^~~~~~~
> > >
> > > ../lib/eal/arm/include/rte_pause_64.h:66:3: note: in expansion of macro
> > > ‘asm’
> > > 66 | asm volatile("ldaxr %w[tmp], [%x[addr]]" \
> > > | ^~~
> > >
> > > ../lib/eal/arm/include/rte_pause_64.h:96:3: note: in expansion of macro
> > > ‘__LOAD_EXC_32’
> > > 96 | __LOAD_EXC_32((src), dst, memorder) \
> > > | ^~~~~~~~~~~~~
> > >
> > > ../lib/eal/arm/include/rte_pause_64.h:167:4: note: in expansion of macro
> > > ‘__LOAD_EXC’
> > > 167 | __LOAD_EXC((addr), value, memorder, size) \
> > > | ^~~~~~~~~~
> > >
> > > ../lib/bpf/bpf_pkt.c:125:3: note: in expansion of macro ‘rte_wait_event’
> > > 125 | rte_wait_event(&cbi->use, UINT32_MAX, ==, puse,
> > > -----------------------------------------------------------------------
> > >
> > > Signed-off-by: Feifei Wang <feifei.wa...@arm.com>
> > > Reviewed-by: Ruifeng Wang <ruifeng.w...@arm.com>
> > > ---
> > > lib/bpf/bpf_pkt.c | 11 ++++-------
> > > 1 file changed, 4 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/lib/bpf/bpf_pkt.c b/lib/bpf/bpf_pkt.c index
> > > 6e8248f0d6..213d44a75a 100644
> > > --- a/lib/bpf/bpf_pkt.c
> > > +++ b/lib/bpf/bpf_pkt.c
> > > @@ -111,9 +111,9 @@ bpf_eth_cbi_unuse(struct bpf_eth_cbi *cbi)
> > > * Waits till datapath finished using given callback.
> > > */
> > > static void
> > > -bpf_eth_cbi_wait(const struct bpf_eth_cbi *cbi)
> > > +bpf_eth_cbi_wait(struct bpf_eth_cbi *cbi)
> >
> > Hi, Konstantin
> >
> > For this bpf patch, I delete 'const' through this is contrary to what we
> > discussed earlier. This is because if we keep 'constant' here and use
> > 'rte_wait_event'
> > new macro, compiler will report error. And earlier the arm version cannot
> > be compiled
> > due to I forgot enable "wfe" config in the meson file, so this issue can
> > not happen before.
>
>
> Honestly, I don't understand why we have to remove perfectly valid 'const'
> qualifier here.
> If this macro can't be used with pointers to const (still don't understand
> why),
> then let's just not use this macro here.
> Strictly speaking I don't see much benefit here from it.
>
> >
> > > {
> > > - 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_wait_event(&cbi->use, UINT32_MAX, ==, puse,
> > > + __ATOMIC_RELAXED);
After another thought, if we do type conversion at macro invocation time:
bpf_eth_cbi_wait(const struct bpf_eth_cbi *cbi)
{
...
rte_wait_event((uint32_t *)&cbi->use, UINT32_MAX, ==, puse, __ATOMIC_RELAXED);
would that help?
> > > }
> > > }
> > >
> > > --
> > > 2.25.1
