netdev - Re: [PATCH bpf-next v2 4/8] xsk: make xskmap flush

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Message-ID: <CAJ+HfNiQOpAbHHT9V-gcp9u=vVDoP6uSoz2f-diEFrfX_88pMg@mail.gmail.com>
Date:   Wed, 8 Jan 2020 11:13:34 +0100
From:   Björn Töpel <bjorn.topel@...il.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     Netdev <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Björn Töpel <bjorn.topel@...el.com>,
        bpf <bpf@...r.kernel.org>, David Miller <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>
Subject: Re: [PATCH bpf-next v2 4/8] xsk: make xskmap flush_list common for
 all map instances

On Tue, 7 Jan 2020 at 18:54, John Fastabend <john.fastabend@...il.com> wrote:
>
> Björn Töpel wrote:
> > From: Björn Töpel <bjorn.topel@...el.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@...hat.com>
> > Signed-off-by: Björn Töpel <bjorn.topel@...el.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?


Björn


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