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

[Eelco Chaudron <echaudro@redhat.com>]

On 19/09/17 09:28, Olivier MATZ wrote:
> Hi,
>
> On Thu, Sep 14, 2017 at 09:22:38AM +0200, Eelco Chaudron wrote:
>> On 13/09/17 11:39, Thomas Monjalon wrote:
>>> 12/09/2017 15:08, Eelco Chaudron:
>>>> 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.
>>> Does it work on FreeBSD?
>> I do not have a FreeBSD setup, but from the documentation I've read the call
>> is supported by FreeBSD.
>> If some one has a working setup, please give this patch a quick try.
>>> Is there any drawback?
>>> Do we need to add an option for it?
>> The only drawback I can think of is that with this change memory phyiscal
>> memory is consumed as pages are pre-loaded.
>> For testpmd (just loaded not doing anything) this is 2MB vs 35MB of memory
>> used. I do not think this yields an extra option.
> One small comment: the call to mlockall() will fail if we don't have
> the permissions. I guess it's not an issue, but I wonder if we should
> log it?
I did not at add a log, as the rte log subsystem is not yet initialized.
However we could add a printf("WARNING: mlockall() failed with error %s")
like message. What do you think?

> Olivier