netdev - Re: [PATCH bpf-next 00/13] bpf: adding map batch processing support

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Date:   Thu, 29 Aug 2019 17:15:13 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Brian Vazquez <brianvv@...gle.com>
Cc:     Yonghong Song <yhs@...com>, Alexei Starovoitov <ast@...com>,
        bpf@...r.kernel.org, netdev@...r.kernel.org,
        Daniel Borkmann <daniel@...earbox.net>, kernel-team@...com
Subject: Re: [PATCH bpf-next 00/13] bpf: adding map batch processing support

On Thu, 29 Aug 2019 16:13:59 -0700, Brian Vazquez wrote:
> > We need a per-map implementation of the exec side, but roughly maps
> > would do:
> >
> >         LIST_HEAD(deleted);
> >
> >         for entry in map {
> >                 struct map_op_ctx {
> >                         .key    = entry->key,
> >                         .value  = entry->value,
> >                 };
> >
> >                 act = BPF_PROG_RUN(filter, &map_op_ctx);
> >                 if (act & ~ACT_BITS)
> >                         return -EINVAL;
> >
> >                 if (act & DELETE) {
> >                         map_unlink(entry);
> >                         list_add(entry, &deleted);
> >                 }
> >                 if (act & STOP)
> >                         break;
> >         }
> >
> >         synchronize_rcu();
> >
> >         for entry in deleted {
> >                 struct map_op_ctx {
> >                         .key    = entry->key,
> >                         .value  = entry->value,
> >                 };
> >
> >                 BPF_PROG_RUN(dumper, &map_op_ctx);
> >                 map_free(entry);
> >         }
> >  
> Hi Jakub,
> 
> how would that approach support percpu maps?
> 
> I'm thinking of a scenario where you want to do some calculations on
> percpu maps and you are interested on the info on all the cpus not
> just the one that is running the bpf program. Currently on a pcpu map
> the bpf_map_lookup_elem helper only returns the pointer to the data of
> the executing cpu.

Right, we need to have the iteration outside of the bpf program itself,
and pass the element in through the context. That way we can feed each
per cpu entry into the program separately.