Re: DPDK and energy efficiency

[Etienne-Victor Depasquale <edepa () ieee org>]

> This comes from OVS code and shows OVS thread spinning, not DPDK PMD.
> Blame the OVS application for not using e.g. _mm_pause() and burning
> the CPU like crazy.


OK, I'm citing a bit more from the same reference:
*"By tracing back to the function’s caller *
*in the PMD thread main(void *f_), *
we found that the thread kept spinning on the following code block:
for ( ; ; ) {
for ( i = 0; i < poll_cnt; i ++) {
dp_netdev_process_rxq_port (pmd, list[i].port, poll_list[i].rx) ;
}
}
This indicates that the [PMD] thread was continuously
monitoring and executing the receiving data path."

Cheers,

Etienne

On Tue, Feb 23, 2021 at 10:33 PM Pawel Malachowski <
pawmal-nanog () freebsd lublin pl> wrote:

> > > No, it is not PMD that runs the processor in a polling loop.
> > > It is the application itself, thay may or may not busy loop,
> > > depending on application programmers choice.
> >
> > From one of my earlier references [2]:
> >
> > "we found that a poll mode driver (PMD)
> > thread accounted for approximately 99.7 percent
> > CPU occupancy (a full core utilization)."
> >
> > And further on:
> >
> > "we found that the thread kept spinning on the following code block:
> >
> > *for ( ; ; ) {for ( i = 0; i < poll_cnt; i ++)
> {dp_netdev_process_rxq_port
> > (pmd, list[i].port, poll_list[i].rx) ;}}*
> > This indicates that the thread was continuously
> > monitoring and executing the receiving data path."
>
> This comes from OVS code and shows OVS thread spinning, not DPDK PMD.
> Blame the OVS application for not using e.g. _mm_pause() and burning
> the CPU like crazy.
>
>
> For comparison, take a look at top+i7z output from DPDK-based 100G DDoS
> scrubber currently lifting some low traffic using cores 1-13 on 16 core
> host. It uses naive DPDK::rte_pause() throttling to enter C1.
>
> Tasks: 342 total,   1 running, 195 sleeping,   0 stopped,   0 zombie
> %Cpu(s):  6.6 us,  0.6 sy,  0.0 ni, 89.7 id,  3.1 wa,  0.0 hi,  0.0 si,
> 0.0 st
>
>         Core [core-id]  :Actual Freq (Mult.)      C0%   Halt(C1)%  C3 %
>  C6 %  Temp      VCore
>         Core 1 [0]:       1467.73 (14.68x)      2.15    5.35       1
> 92.3    43      0.6724
>         Core 2 [1]:       1201.09 (12.01x)      11.7    93.9       0
>  0    39      0.6575
>         Core 3 [2]:       1200.06 (12.00x)      11.8    93.8       0
>  0    42      0.6543
>         Core 4 [3]:       1200.14 (12.00x)      11.8    93.8       0
>  0    41      0.6549
>         Core 5 [4]:       1200.10 (12.00x)      11.8    93.8       0
>  0    41      0.6526
>         Core 6 [5]:       1200.12 (12.00x)      11.8    93.8       0
>  0    40      0.6559
>         Core 7 [6]:       1201.01 (12.01x)      11.8    93.8       0
>  0    41      0.6559
>         Core 8 [7]:       1201.02 (12.01x)      11.8    93.8       0
>  0    43      0.6525
>         Core 9 [8]:       1201.00 (12.01x)      11.8    93.8       0
>  0    41      0.6857
>         Core 10 [9]:      1201.04 (12.01x)      11.8    93.8       0
>  0    40      0.6541
>         Core 11 [10]:     1201.95 (12.02x)      13.6    92.9       0
>  0    40      0.6558
>         Core 12 [11]:     1201.02 (12.01x)      11.8    93.8       0
>  0    42      0.6526
>         Core 13 [12]:     1204.97 (12.05x)      17.6    90.8       0
>  0    45      0.6814
>         Core 14 [13]:     1248.39 (12.48x)      28.2    84.7       0
>  0    41      0.6855
>         Core 15 [14]:     2790.74 (27.91x)      91.9       0       1
>  1    41      0.8885 <-- not PMD
>         Core 16 [15]:     1262.29 (12.62x)      13.1    34.9     1.7
> 56.2    43      0.6616
>
> $ dataplanectl stats fcore | grep total
> fcore total idle 393788223887 work 860443658 (0.2%) (forced-idle
> 7458486526622) recv 202201388561 drop 61259353721 (30.3%) limit 269909758
> (0.1%) pass 140606076622 (69.6%) ingress 66048460 (0.0%/0.0%) sent
> 162580376914 (80.4%/100.0%) overflow 0 (0.0%) sampled 628488188/628488188
>
>
>
> --
> Pawel Malachowski
> @pawmal80


-- 
Ing. Etienne-Victor Depasquale
Assistant Lecturer
Department of Communications & Computer Engineering
Faculty of Information & Communication Technology
University of Malta
Web. https://www.um.edu.mt/profile/etiennedepasquale