[dpdk-dev] 回复: [PATCH v5 4/5] lib/bpf: use wait event scheme for Rx/Tx iteration

[Feifei Wang]

> -----邮件原件-----
> 发件人: Feifei Wang <feifei.wang2 at arm.com>
> 发送时间: Tuesday, October 26, 2021 4:02 PM
> 收件人: Konstantin Ananyev <konstantin.ananyev at intel.com>
> 抄送: dev at dpdk.org; nd <nd at arm.com>; Feifei Wang
> <Feifei.Wang2 at arm.com>; Ruifeng Wang <Ruifeng.Wang at arm.com>
> 主题: [PATCH v5 4/5] lib/bpf: use wait event scheme for Rx/Tx iteration
> 
> 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.wang2 at arm.com>
> Reviewed-by: Ruifeng Wang <ruifeng.wang at 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.

>  {
> -	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);
>  	}
>  }
> 
> --
> 2.25.1