Re: [dpdk-dev] [PATCH v2 5/7] bpf: introduce basic RX/TX BPF filters

[Jerin Jacob <jerin.jacob@caviumnetworks.com>]

-----Original Message-----
> Date: Fri, 30 Mar 2018 18:32:41 +0100
> From: Konstantin Ananyev <konstantin.ananyev@intel.com>
> To: dev@dpdk.org
> CC: Konstantin Ananyev <konstantin.ananyev@intel.com>
> Subject: [dpdk-dev] [PATCH v2 5/7] bpf: introduce basic RX/TX BPF filters
> X-Mailer: git-send-email 1.7.0.7
> 
> Introduce API to install BPF based filters on ethdev RX/TX path.
> Current implementation is pure SW one, based on ethdev RX/TX
> callback mechanism.
> 
> Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
> ---

Hi Konstantin,

> +/*
> + * Marks given callback as used by datapath.
> + */
> +static __rte_always_inline void
> +bpf_eth_cbi_inuse(struct bpf_eth_cbi *cbi)
> +{
> +	cbi->use++;
> +	/* make sure no store/load reordering could happen */
> +	rte_smp_mb();
> +}
> +
> +/*
> + * Marks given callback list as not used by datapath.
> + */
> +static __rte_always_inline void
> +bpf_eth_cbi_unuse(struct bpf_eth_cbi *cbi)
> +{
> +	/* make sure all previous loads are completed */
> +	rte_smp_rmb();

We earlier discussed this barrier. Will following scheme works out to
fix the bpf_eth_cbi_wait() without cbi->use scheme?

#ie. We need to exit from jitted or interpreted code irrespective of its
state. IMO, We can do that by an _arch_ specific function to fill jitted  memory with
"exit" opcode(value:0x95, exit, return r0),so that above code needs to be come out i n anycase,
on next instruction execution. I know, jitted memory is read-only in your
design, I think, we can change the permission to "write" to the fill
"exit" opcode(both jitted or interpreted case) for termination.


What you think?

> +	cbi->use++;
> +}
> +
> +/*
> + * Waits till datapath finished using given callback.
> + */
> +static void
> +bpf_eth_cbi_wait(const struct bpf_eth_cbi *cbi)
> +{
> +	uint32_t nuse, puse;
> +
> +	/* make sure all previous loads and stores are completed */
> +	rte_smp_mb();
> +
> +	puse = cbi->use;
> +
> +	/* 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);
> +	}
> +}