[dpdk-users] Lcore impact

Александр Киселев kiselev99 at gmail.com
Thu Apr 14 21:31:01 CEST 2016

2016-04-14 20:49 GMT+03:00 Hu, Xuekun <xuekun.hu at intel.com>:

> Are the two lcore belonging to one processor, or two processors? What the
> memory footprint is for the system call threads? If the memory footprint is
> big (>LLC cache size) and two locre are in the same processor, then it
> could have impact on packet processing thread.

Those two lcores belong to one processor and it's a single processor

Both cores allocates a lot of memory and use the full dpdk arsenal: lpm,
mempools, hashes and etc. But during the test the core doing socket data
transfering is using only small 16k buffer for sending and sending is the
all it does during the test. It doesn't use any other allocated memory
structures. The processing core in turn is using rte_lpm whitch is big, but
in my test there are only about 10 routes in it, so I think the amount
"hot" memory is not very big. But I can't say if it's bigger than l3 cpu
cache or not. Should I use some profilers and see if socket operations
cause a lot of cache miss in the processing lcore? It there some tool that
allows me to do that? perf maybe?

> -----Original Message-----
> From: users [mailto:users-bounces at dpdk.org] On Behalf Of Alexander Kiselev
> Sent: Friday, April 15, 2016 1:19 AM
> To: Shawn Lewis
> Cc: users at dpdk.org
> Subject: Re: [dpdk-users] Lcore impact
> I've already seen this documen and have used this tricks a lot of times.
> But this time I send data locally over localhost. There is even no nics
> bind to linux in my machine. Therefore there is no nics interruptions I can
> pin to cpu. So what do you propose?
> > 14 апр. 2016 г., в 20:06, Shawn Lewis <smlsr at tencara.com> написал(а):
> >
> > You have to work with IRQBalancer as well
> >
> >
> http://www.intel.com/content/dam/doc/application-note/82575-82576-82598-82599-ethernet-controllers-interrupts-appl-note.pdf
> >
> > Is just an example document which discuss this (not so much DPDK
> related)...  But the OS will attempt to balance the interrupts when you
> actually want to remove or pin them down...
> >
> >> On Thu, Apr 14, 2016 at 1:02 PM, Alexander Kiselev <kiselev99 at gmail.com>
> wrote:
> >>
> >>
> >>> 14 апр. 2016 г., в 19:35, Shawn Lewis <smlsr at tencara.com> написал(а):
> >>>
> >>> Lots of things...
> >>>
> >>> One just because you have a process running on an lcore, does not mean
> thats all that runs on it.  Unless you have told the kernel at boot to NOT
> use those specific cores, those cores will be used for many things OS
> related.
> >>
> >> Generally yes, but unless I start sending data to socket there is no
> packet loss.  I did about 10 test runs in a raw and everythis was ok. And
> there is no other application running on that test machine that uses cpu
> cores.
> >>
> >> So the question is why this socket operations influence the other lcore?
> >>
> >>>
> >>> IRQBlance
> >>> System OS operations.
> >>> Other Applications.
> >>>
> >>> So by doing file i/o you are generating interrupts, where those
> interrupts get serviced is up to IRQBalancer.  So could be any one of your
> cores.
> >>
> >> That is a good point. I can use cpu affinity feature to bind
> unterruption handler to the core not used in my test. But I send data
> locally over localhost. Is it possible to use cpu affinity in that case?
> >>
> >>>
> >>>
> >>>
> >>>> On Thu, Apr 14, 2016 at 12:31 PM, Alexander Kiselev <
> kiselev99 at gmail.com> wrote:
> >>>> Could someone give me any hints about what could cause permormance
> issues in a situation where one lcore doing a lot of linux system calls
> (read/write on socket) slow down the other lcore doing packet forwarding?
> In my test the forwarding lcore doesn't share any memory structures with
> the other lcore that sends test data to socket. Both lcores pins to
> different processors cores. So therotically they shouldn't have any impact
> on each other but they do, once one lcore starts sending data to socket the
> other lcore starts dropping packets. Why?
> >>>
> >

С уважением,
Киселев Александр

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