Re: [RFC PATCH 10/12] xdp: Add batching support to redirect map

[John Fastabend]

On 07/10/2017 10:53 AM, Jesper Dangaard Brouer wrote:
> On Fri, 07 Jul 2017 10:37:59 -0700
> John Fastabend  wrote:
> 
>> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
>> index 36dc13de..656e334 100644
>> --- a/kernel/bpf/devmap.c
>> +++ b/kernel/bpf/devmap.c
> [...]
>>  
>> +void __dev_map_insert_ctx(struct bpf_map *map, u32 key)
>> +{
>> +struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
>> +unsigned long *bitmap = this_cpu_ptr(dtab->flush_needed);
>> +
>> +set_bit(key, bitmap);
>> +}
> 
> I don't like that this adds an atomic op (set_bit) per packet on a fast-path.
> It shows up on a perf top #6 with xdp_redirect_map.
> 

Its a per cpu bitmap so __set_bit() should be fine here.

Thanks,
John

Re: [RFC PATCH 10/12] xdp: Add batching support to redirect map

[Jesper Dangaard Brouer]

On Fri, 07 Jul 2017 10:37:59 -0700
John Fastabend  wrote:

> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
> index 36dc13de..656e334 100644
> --- a/kernel/bpf/devmap.c
> +++ b/kernel/bpf/devmap.c
[...]
>  
> +void __dev_map_insert_ctx(struct bpf_map *map, u32 key)
> +{
> + struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
> + unsigned long *bitmap = this_cpu_ptr(dtab->flush_needed);
> +
> + set_bit(key, bitmap);
> +}

I don't like that this adds an atomic op (set_bit) per packet on a fast-path.
It shows up on a perf top #6 with xdp_redirect_map.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer