> -Original Message-
> From: Jon Maloy
> Sent: Thursday, September 9, 2021 5:42 AM
> To: Hoang Huu Le ;
> tipc-discussion@lists.sourceforge.net; Tung Quang Nguyen
> ; Xin Long ; Ying Xue
>
> Cc: Huy Xuan Nhat Hoang
> Subject: Re: Strange behavior in socket.c::tipc_sk_enqueue()
>
>
>
> On 06/09/2021 05:02, Hoang Huu Le wrote:
> > Hi Jon, all,
> >
> > I did a test by setting two variables condition in range:
> > - time limit: 2 msecs ... unlimited
> > - search depth limit (sock's skbs): 2 skbs ... unlimited
> >
> > With above range settings, a maximum sock's skbs can be enqueued around 12
> > skbs regardless of time and search depth limit.
> > I also combine the test with iperf TCP traffic generated and the result
> > looks the same.
> >
> > So, I don't think we need to apply the search depth limit condition and/or
> > longer timer in this function, just 2msecs is enough.
> > I guess this result depends on kernel schedule. What are your views?
>
> I assume your test was done with many, e.g. 100 connections?
Yes, I did the test from 1 to 150 connections and combine with/out other
traffic generate (i.e TCP).
>
> ///jon
>
> >
> > Regards,
> > Hoang
> >> -Original Message-
> >> From: Jon Maloy
> >> Sent: Wednesday, September 1, 2021 7:39 AM
> >> To: Hoang Huu Le ;
> >> tipc-discussion@lists.sourceforge.net; Tung Quang Nguyen
> >> ; Xin Long ; Ying Xue
> >>
> >> Cc: Huy Xuan Nhat Hoang
> >> Subject: Re: Strange behavior in socket.c::tipc_sk_enqueue()
> >>
> >> Guys,
> >> After our discussion this morning regarding this problem I gave it some
> >> more thought.
> >>
> >> What if we simply limit the search depth in the receive queue to some
> >> fix number, 10, 20, 50 or something and return NULL if nothing is found
> >> within this range. This would be a simple stack counter inside
> >> tipc_skb_dequeue(), and would cost almost nothing.
> >>
> >> If you experiment with this, of course in combination with a max limit
> >> of some milliseconds as we also discussed, we might obtain acceptable
> >> results.
> >>
> >> What do you think?
> >>
> >> ///jon
> >>
> >>
> >> On 28/07/2021 04:04, Hoang Huu Le wrote:
> >>> Hi Jon,
> >>>
> >>> Let's enjoy your vacation.
> >>> Our new team member (CCed) will take a look at it.
> >>>
> >>> Regards,
> >>> Hoang
> -Original Message-
> From: Jon Maloy
> Sent: Wednesday, July 28, 2021 6:20 AM
> To: tipc-discussion@lists.sourceforge.net; Tung Quang Nguyen
> ; Hoang Huu Le
> ; Xin Long ; Ying Xue
>
> Subject: Strange behavior in socket.c::tipc_sk_enqueue()
>
> I did by accident discover a strange behavior in the function
> tipc_sk_enqueue:
>
>
> static void tipc_sk_enqueue(struct sk_buff_head *inputq,
> struct sock *sk, u32 dport,
> struct sk_buff_head *xmitq)
> {
> struct tipc_sock *tsk = tipc_sk(sk);
> unsigned long time_limit = jiffies + 2;
> struct sk_buff *skb;
> unsigned int lim;
> atomic_t *dcnt;
> u32 onode;
>
> while (skb_queue_len(inputq)) {
> if (unlikely(time_after_eq(jiffies, time_limit)))
> return;
> [...]
> }
> }
>
> At the moment we call time_after_eq() the two jiffies often
> have already passed, and the skb is not dequeued.
> I noticed that tipc_sk_rcv() may call tipc_sk_enqueue()
> with the same skb dozens of times before the buffer can
> be delivered further upwards in the stack.
>
> Needless to say that this cannot be good for performance.
>
> I believe the value of 2 jiffies was hard coded at a time
> when machines were slower, and a jiffie represented a much
> longer time interval.
>
> Now it is clearly too short, and should be replaced with something
> longer and more consisten, e.g. msec_to_jiffies(2).
>
> Can anybody look into this?
>
> Also, I will be on vacation the next two weeks, which means we
> should cancel the bi-weekly meeting next Tuesday.
>
> ///jon
>
> >>>
> >
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