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

[Olivier MATZ <olivier.matz@6wind.com>]

On Thu, Sep 21, 2017 at 02:24:28PM +0200, Eelco Chaudron wrote:
> 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?

Since it's not critical, maybe NOTICE is better than WARNING.

One more question: what would be the drawback of calling
mlockall() after eal_init()? (rte_log would be initialized)


Thanks,
Olivier