[dpdk-dev] [PATCH] app/testpmd: adds mlockall() to fix pages

Aaron Conole aconole at redhat.com
Tue Sep 12 22:29:11 CEST 2017

Thomas Monjalon <thomas at monjalon.net> writes:

> 12/09/2017 16:50, Aaron Conole:
>> Eelco Chaudron <echaudro at redhat.com> writes:
>> > Call the mlockall() function, to attempt to lock all of its process
>> > memory into physical RAM, and preventing the kernel from paging any
>> > of its memory to disk.
>> >
>> > When using testpmd for performance testing, depending on the code path
>> > taken, we see a couple of page faults in a row. These faults effect
>> > the overall drop-rate of testpmd. On Linux the mlockall() call will
>> > prefault all the pages of testpmd (and the DPDK libraries if linked
>> > dynamically), even without LD_BIND_NOW.
>> >
>> > Signed-off-by: Eelco Chaudron <echaudro at redhat.com>
>> Acked-by: Aaron Conole <aconole at redhat.com>
> It is interesting, but why make it in testpmd?
> Maybe it should be documented in this guide:
> 	http://dpdk.org/doc/guides/linux_gsg/nic_perf_intel_platform.html

Well, I'm not sure what the user would be able to do to get the
prefaulting performance without having a library they use with
LD_PRELOAD and a function with the constructor attribute which does the
same thing, AND export LD_BIND_NOW before linking starts.

The LD_BIND_NOW simply does the symbol resolution, but there's no
guarantee that it will fault all the code pages in to process space, and
without an mlockall(), I'm not sure that there's any kind of guarantee
that they don't get swapped out of resident memory (which also leads to
later page faults).

Maybe I misunderstood the question?

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