From: Jamal Hadi Salim <jhs@mojatatu•com>
To: Jesper Dangaard Brouer <brouer@redhat•com>
Cc: David Miller <davem@davemloft•net>,
netdev@vger•kernel.org, therbert@google•com,
hannes@stressinduktion•org, edumazet@google•com,
jeffrey.t.kirsher@intel•com, rusty@rustcorp•com.au,
dborkman@redhat•com
Subject: Re: [PATCH 0/2] Get rid of ndo_xmit_flush
Date: Tue, 26 Aug 2014 10:40:28 -0400 [thread overview]
Message-ID: <53FC9C5C.1070200@mojatatu.com> (raw)
In-Reply-To: <20140826121347.0ec7f2ac@redhat.com>
On 08/26/14 06:13, Jesper Dangaard Brouer wrote:
>
> On Tue, 26 Aug 2014 08:28:15 +0200 Jesper Dangaard Brouer <brouer@redhat•com> wrote:
>> On Mon, 25 Aug 2014 16:34:58 -0700 (PDT) David Miller <davem@davemloft•net> wrote:
>>
>>> Given Jesper's performance numbers, it's not the way to go.
>>>
>>> Instead, go with a signalling scheme via new boolean skb->xmit_more.
>>
>> I'll do benchmarking based on this new API proposal today.
>
> While establish an accurate baseline for my measurements. I'm
> starting to see too much variation in my trafgen measurements.
> Meaning that we unfortunately cannot use it to measure variations on
> the nanosec scale.
>
> I'm measuring the packets per sec via "ifpps", and calculating an
> average over the measurements, via the following oneliner:
>
> $ ifpps -clod eth5 -t 1000 | awk 'BEGIN{txsum=0; rxsum=0; n=0} /[[:digit:]]/ {txsum+=$11;rxsum+=$3;n++; printf "instant rx:%u tx:%u pps n:%u average: rx:%d tx:%d pps\n", $3, $11, n, rxsum/n, txsum/n }'
>
> Below is measurements done on the *same* kerne:
> - M1: instant tx:1572766 pps n:215 average: tx:1573360 pps (reboot#1)
> - M2: instant tx:1561930 pps n:173 average: tx:1557064 pps (reboot#2)
> - M3: instant tx:1562088 pps n:300 average: tx:1559150 pps (reboot#2)
> - M4: instant tx:1564404 pps n:120 average: tx:1564948 pps (reboot#3)
>
> M1->M2: +6.65ns
> M1->M3: +5.79ns
> M1->M4: +3.42ns
> M3->M4: -2.38ns
>
> I cannot explain the variations, but some options could be
> 1) how well the SKB is cache-hot cached via kmem_cache
> 2) other interrups on CPU#0 could disturb us
> 3) interactions with scheduler
> 4) interactions with transparent hugepages
> 5) CPU "turbostat" interactions
>
The clock source used in your system may be an issue as well.
I am not sure if that matters these days but it used to be.
I think back then you could pick ACPI, Jiffies etc to use
as a qdisc clock source.
cheers,
jamal
next prev parent reply other threads:[~2014-08-26 14:40 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-25 23:34 [PATCH 0/2] Get rid of ndo_xmit_flush David Miller
2014-08-26 6:28 ` Jesper Dangaard Brouer
2014-08-26 10:13 ` Jesper Dangaard Brouer
2014-08-26 12:52 ` Jesper Dangaard Brouer
2014-08-26 16:43 ` Alexander Duyck
2014-08-27 7:48 ` Jesper Dangaard Brouer
2014-08-27 8:37 ` Jesper Dangaard Brouer
2014-08-26 14:40 ` Jamal Hadi Salim [this message]
2014-09-01 0:37 ` Rusty Russell
2014-08-27 12:19 ` Jesper Dangaard Brouer
2014-08-27 20:43 ` David Miller
2014-08-27 12:31 ` Hannes Frederic Sowa
2014-08-27 13:23 ` Eric Dumazet
2014-08-27 13:56 ` Jesper Dangaard Brouer
2014-08-27 14:09 ` Eric Dumazet
2014-08-27 20:48 ` David Miller
2014-08-27 20:46 ` David Miller
2014-08-27 20:45 ` David Miller
2014-08-28 1:42 ` Hannes Frederic Sowa
2014-08-30 3:22 ` David Miller
2014-08-30 10:23 ` Jesper Dangaard Brouer
2014-09-01 20:05 ` Hannes Frederic Sowa
2014-09-01 21:56 ` David Miller
2014-09-01 22:31 ` Hannes Frederic Sowa
2014-09-01 22:35 ` David Miller
2014-08-27 18:28 ` Cong Wang
2014-08-27 19:31 ` Tom Herbert
2014-08-27 20:53 ` David Miller
2014-08-27 20:51 ` David Miller
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