On Mon, 2017-11-06 at 14:48 +0800, Liu Yu wrote:
> On Mon, Nov 6, 2017 at 1:27 PM, Eric Dumazet <[email protected]> wrote:
> > On Mon, 2017-11-06 at 10:28 +0800, Liu Yu wrote:
> >> From: Liu Yu <[email protected]>
> >>
> >> When a mount of processes connect to the same port at the same address
> >> simultaneously, they are likely getting the same bhash and therefore
> >> conflict with each other.
> >>
> >> The more the cpu number, the worse in this case.
> >>
> >> Use spin_trylock instead for this scene, which seems doesn't matter
> >> for common case.
> >>
> >> Signed-off-by: Liu Yu <[email protected]>
> >> ---
> >> net/ipv4/inet_hashtables.c | 6 +++++-
> >> 1 files changed, 5 insertions(+), 1 deletions(-)
> >>
> >> diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
> >> index e7d15fb..cc11ec7 100644
> >> --- a/net/ipv4/inet_hashtables.c
> >> +++ b/net/ipv4/inet_hashtables.c
> >> @@ -581,13 +581,17 @@ int __inet_hash_connect(struct
> >> inet_timewait_death_row *death_row,
> >> other_parity_scan:
> >> port = low + offset;
> >> for (i = 0; i < remaining; i += 2, port += 2) {
> >> + int ret;
> >> +
> >> if (unlikely(port >= high))
> >> port -= remaining;
> >> if (inet_is_local_reserved_port(net, port))
> >> continue;
> >> head = &hinfo->bhash[inet_bhashfn(net, port,
> >> hinfo->bhash_size)];
> >> - spin_lock_bh(&head->lock);
> >> + ret = spin_trylock(&head->lock);
> >> + if (unlikely(!ret))
> >> + continue;
> >>
> >> /* Does not bother with rcv_saddr checks, because
> >> * the established check is already unique enough.
> >
> > This is broken.
> >
> > I am pretty sure you have not really tested this patch properly.
> >
> > Chances are very high that a connect() will miss slots and wont succeed,
> > when table is almost full.
>
> Thanks for your comments!
>
> Can you explain how connect() miss slots when table is almost full?
Every time your spin_trylock() is failing, you will not examin one port.
Now go back to the loop :
for (i = 0; i < remaining; i += 2, port += 2) {
Since we no longer look all the ports, we are going to fail to find a
4-tuple.
Really a spin_trylock() is a not a good idea.
Find something else if you really have contention at connect()
>
> >
> > Performance is nice, but we actually need to allocate a 4-tuple in a
> > more deterministic fashion.
> >
>
> So, what's the 4th element would you suggest?
What 4th element I am suggesting ?
