netdev - Re: [RFC PATCH] ip: re-introduce fragments cache worker

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Date:   Fri, 6 Jul 2018 07:20:45 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Florian Westphal <fw@...len.de>, NeilBrown <neilb@...e.com>
Subject: Re: [RFC PATCH] ip: re-introduce fragments cache worker



On 07/06/2018 06:56 AM, Paolo Abeni wrote:
> On Fri, 2018-07-06 at 05:09 -0700, Eric Dumazet wrote:
>> On 07/06/2018 04:56 AM, Paolo Abeni wrote:
>>> With your setting, you need a bit more concurrent connections (400 ?)
>>> to saturate the ipfrag cache. Above that number, performances will
>>> still sink.
>>
>> Maybe, but IP defrag can not be 'perfect'.
>>
>> For this particular use case I could still bump high_thresh to 6 GB and all would be good :)
> 
> Understood.
> 
> I'd like to be sure I stated the problem I see clearly. With the
> current code the "goodput" goes to almost 0 as soon as the ipfrag cache
> load goes above it's capacity. Before the worker removal, after
> reaching high_thresh, the "goodput" degratated slowly and even with a
> load more than an order of magnitude higher, the performances were
> still quite good. I think we can't ask customers to add more memory for
> a kernel upgrade; even changing the default sysfs configuration is
> somewhat troubling.
> 
>>> This looks nice, I'll try to test it in my use case and I'll report
>>> here.
> 
> I tried the patch, but the result are not encouraging:
> 
> ./super_netperf.sh 200 -H 192.168.101.2 -t UDP_STREAM -l 60
> 34.94
> 
> # on the receiver side:
> echo 2 >  /proc/sys/net/ipv4/ipfrag_time
> 
> # on the sender side:
> ./super_netperf.sh 200 -H 192.168.101.2 -t UDP_STREAM -l 60
> 85.8
> 
> # still on receiver side, while the test is running:
> nstat>/dev/null ;sleep 1; nstat |grep IpReasm
> IpReasmTimeout                  2128               0.0
> IpReasmReqds                    754770             0.0
> IpReasmOKs                      135                0.0
> IpReasmFails                    752811             0.0
> 
> grep FRAG /proc/net/sockstat
> FRAG: inuse 124 memory 5286144
> 
> The patch has some effect, as I basically saw no timeout without it,
> but still does not look aggressive enough. Or possibly it's evicting
> the fragments that are more likely to be used/completed (the most
> recents one).

Hey, that was simply an idea (not even compiled), not the final patch.

I will test/polish it later, I am coming back from vacations and have a backlog.

Here are my results : (Note that I have _not_ changed /proc/sys/net/ipv4/ipfrag_time )

lpaa6:~# grep . /proc/sys/net/ipv4/ipfrag_* ; grep FRAG /proc/net/sockstat
/proc/sys/net/ipv4/ipfrag_high_thresh:104857600
/proc/sys/net/ipv4/ipfrag_low_thresh:78643200
/proc/sys/net/ipv4/ipfrag_max_dist:0
/proc/sys/net/ipv4/ipfrag_secret_interval:0
/proc/sys/net/ipv4/ipfrag_time:30
FRAG: inuse 1379 memory 105006776

lpaa5:/export/hda3/google/edumazet# ./super_netperf 400 -H 10.246.7.134 -t UDP_STREAM -l 60
netperf: send_omni: send_data failed: No route to host
netperf: send_omni: send_data failed: No route to host
   9063


I would say that it looks pretty good to me.