[dpdk-dev] Number of memory channels (EAL Options)

[Muhammad Ali]

Thanks for your detailed reply, I just want to clear myself on Number of
Memory Channels, These Memory channels are between

CPU and Hugepages (RAM)
or
HugePages (RAM) and NIC   (multi channel DMA)
or
both

?

Thanks


On Thu, Jun 20, 2013 at 8:43 PM, Stephen Hemminger <
stephen at networkplumber.org> wrote:

> On Thu, 20 Jun 2013 16:20:35 +0500
> Muhammad Ali <Muhammad.Ali at xflowresearch.com> wrote:
>
> > Hi everyone
> >
> > I am running DPDK sample application compiled in Fedora 14 environment.
> >
> > I have used following command to run the App
> >
> > ./<application> -c f -n 4
> >
> > c= bitmask of cores to to be used.
> > and
> > n= number of memory channels
> >
> > Now what does 'n' actually defines ?. Is this the number of DMA channels
> > between RAM (hugepages) and NIC. ? If not so then what it is ?
> >
> > How does number of memory channels will effect the performance ?
> >
> > BTW I am using hugepagesize=1G
> > and Number of Hugepages=4
> >
> > My question might be very basic, but I am totally confused. Please help
> me
> > out here.
> >
> > Thank you
> >
> > Regards
>
> Memory channels into the CPU, it controls the spread layout used by the
> memory
> allocator, therefore it is a performance optimization.
>
> Unfortunately, there is no good way to know what the number of memory
> channels
> exactly without hardware specs. The BIOS may know but it is not exported
> in any
> of the normal ACPI tables, and therefore not exposed by the OS.
>
> What we end up doing in our startup script was
>  "dmidecode -t 17 | grep -c 'Size:'"
> which will give you some idea of the number of populated memory banks and
> making
> an educated guess on the number of channels. I.e 6 memory slots probably
> implies 3 channels.
> If someone has a better way I would love to hear it.
>
> Computing cpu bitmask isn't hard using "grep -c processor /proc/cpuinfo"
> and a
> little maths in a shell script.
>
>


-- 


Muhammad Ali
Software Development Engineer
xFlow Research Inc. <http://www.xflowresearch.com/>
+92-323-965-4043 (GMT +5)
*Skype: *ali.wcct

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