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From:   Doug Anderson <dianders@chromium.org>
Date:   Wed, 6 Dec 2023 10:49:29 -0800
Message-ID: <CAD=FV=UgPZoXsGTgLV_4X9x2hGTMouO3Tpe9_WkwhU7Bsvav2Q@mail.gmail.com>
Subject: Re: [PATCH v2] neighbour: Don't let neigh_forced_gc() disable
 preemption for long
To:     David Ahern <dsahern@kernel.org>
Cc:     Stephen Hemminger <stephen@networkplumber.org>,
        Judy Hsiao <judyhsiao@chromium.org>,
        Eric Dumazet <edumazet@google.com>,
        Simon Horman <horms@kernel.org>,
        Brian Haley <haleyb.dev@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Joel Granados <joel.granados@gmail.com>,
        Julian Anastasov <ja@ssi.bg>,
        Leon Romanovsky <leon@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org
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Hi,

On Wed, Dec 6, 2023 at 9:51=E2=80=AFAM David Ahern <dsahern@kernel.org> wro=
te:
>
> On 12/6/23 10:39 AM, Stephen Hemminger wrote:
> > On Wed,  6 Dec 2023 03:38:33 +0000
> > Judy Hsiao <judyhsiao@chromium.org> wrote:
> >
> >> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> >> index df81c1f0a570..552719c3bbc3 100644
> >> --- a/net/core/neighbour.c
> >> +++ b/net/core/neighbour.c
> >> @@ -253,9 +253,11 @@ static int neigh_forced_gc(struct neigh_table *tb=
l)
> >>  {
> >>      int max_clean =3D atomic_read(&tbl->gc_entries) -
> >>                      READ_ONCE(tbl->gc_thresh2);
> >> +    u64 tmax =3D ktime_get_ns() + NSEC_PER_MSEC;
> >>      unsigned long tref =3D jiffies - 5 * HZ;
> >>      struct neighbour *n, *tmp;
> >>      int shrunk =3D 0;
> >> +    int loop =3D 0;
> >>
> >>      NEIGH_CACHE_STAT_INC(tbl, forced_gc_runs);
> >>
> >> @@ -278,11 +280,16 @@ static int neigh_forced_gc(struct neigh_table *t=
bl)
> >>                              shrunk++;
> >>                      if (shrunk >=3D max_clean)
> >>                              break;
> >> +                    if (++loop =3D=3D 16) {
> >
> > Overall looks good.
> > Minor comments:
> >       - loop count should probably be unsigned
> >         - the magic constant 16 should be a sysctl tuneable
>
> A tunable is needed here; the loop counter is just to keep the overhead
> of the ktime_get_ns call in check.

From context, I'm going to assume you meant a tunable is _NOT_ needed here.=
 ;-)

-Doug