netdev - Re: [PATCH net-next 0/2] net: broadcom: Adaptive interrupt coalescing

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Date:   Mon, 26 Mar 2018 15:04:13 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Tal Gilboa <talgi@...lanox.com>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, jaedon.shin@...il.com, pgynther@...gle.com,
        opendmb@...il.com, michal.chan@...adcom.com, gospo@...adcom.com,
        saeedm@...lanox.com
Subject: Re: [PATCH net-next 0/2] net: broadcom: Adaptive interrupt coalescing

On 03/26/2018 02:16 PM, Tal Gilboa wrote:
> On 3/23/2018 4:19 AM, Florian Fainelli wrote:
>> Hi all,
>>
>> This patch series adds adaptive interrupt coalescing for the Gigabit
>> Ethernet
>> drivers SYSTEMPORT and GENET.
>>
>> This really helps lower the interrupt count and system load, as
>> measured by
>> vmstat for a Gigabit TCP RX session:
> 
> I don't see an improvement in system load, the opposite - 42% vs. 100%
> for SYSTEMPORT and 85% vs. 100% for GENET. Both with the same bandwidth.

Looks like I did not extract the correct data the load could spike in
both cases (with and without net_dim) up to 100, but averaged over the
transmission I see the following:

GENET without:
 1  0      0 1169568      0  25556    0    0     0     0 130079 62795  2
86 13  0  0

GENET with:
 1  0      0 1169536      0  25556    0    0     0     0 10566 10869  1
21 78  0  0

> Am I missing something? Talking about bandwidth, I would expect 941Mb/s
> (assuming this is TCP over IPv4). Do you know why the reduced interrupt
> rate doesn't improve bandwidth?

I am assuming that this comes down to a latency, still capturing some
pcap files to analyze the TCP session with wireshark and see if that is
indeed what is going on. The test machine is actually not that great

> Also, any effect on the client side (you
> mentioned enabling TX moderation for SYSTEMPORT)?

Yes, on SYSTEMPORT, being the TCP IPv4 client, I have the following:

SYSTEMPORT without:
 2  0      0 191428      0  25748    0    0     0     0 86254  264  0 41
59  0  0

SYSTEMPORT with:
 3  0      0 190176      0  25748    0    0     0     0 45485 31332  0
100  0  0  0

I don't get top to agree with these load results though but it looks
like we just have the CPU spinning more, does not look like a win.

Thanks a lot for taking a look at this Tal!
-- 
Florian