Re: [PATCH bpf-next v2 4/8] xsk: make xskmap flush_list common for all map instances

John Fastabend
2020-01-08T15:52:21Z

Björn Töpel wrote:
> On Tue, 7 Jan 2020 at 18:54, John Fastabend <john.fastabend@gmail.com> wrote:
> >
> > Björn Töpel wrote:
> > > From: Björn Töpel <bjorn.topel@intel.com>
> > >
> > > The xskmap flush list is used to track entries that need to flushed
> > > from via the xdp_do_flush_map() function. This list used to be
> > > per-map, but there is really no reason for that. Instead make the
> > > flush list global for all xskmaps, which simplifies __xsk_map_flush()
> > > and xsk_map_alloc().
> > >
> > > Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
> > > Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
> > > ---
> >
> > Just to check. The reason this is OK is because xdp_do_flush_map()
> > is called from NAPI context and is per CPU so the only entries on
> > the list will be from the current cpu napi context?
>
> Correct!
>
> > Even in the case
> > where multiple xskmaps exist we can't have entries from more than
> > a single map on any list at the same time by my reading.
> >
>
> No, there can be entries from different (XSK) maps. Instead of
> focusing on maps to flush, focus on *entries* to flush. At the end of
> the poll function, all entries (regardless of map origin) will be
> flushed. Makes sense?

Ah OK. This would mean that a single program used multiple maps
though correct? Because we can only run a single BPF program per
NAPI context.

What I was after is checking that semantics haven't changed which
I believe is true, just checking.

>
>
> Björn
>
>
> > LGTM,
> > Acked-by: John Fastabend <john.fastabend@gmail.com>