On Mon, Nov 6, 2017 at 1:27 PM, Eric Dumazet <eric.duma...@gmail.com> wrote:
> On Mon, 2017-11-06 at 10:28 +0800, Liu Yu wrote:
>> From: Liu Yu <allanyu...@tencent.com>
>>
>> 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 <allanyu...@tencent.com>
>> ---
>> 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?
>
> 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?
