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Subject: Re: svn commit: r284959 - in head: . share/man/man4 share/man/man9
 sys/conf sys/dev/glxsb sys/dev/hifn sys/dev/random sys/dev/rndtest
 sys/dev/safe sys/dev/syscons sys/dev/ubsec sys/dev/virtio/random sy...
From: Ian Lepore <ian@freebsd.org>
To: Mark Murray <markm@FreeBSD.org>
Cc: Adrian Chadd <adrian.chadd@gmail.com>, "src-committers@freebsd.org"
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Date: Thu, 16 Jul 2015 08:08:49 -0600
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On Thu, 2015-07-16 at 06:39 +0100, Mark Murray wrote:
> > On 15 Jul 2015, at 23:43, Adrian Chadd <adrian.chadd@gmail.com> wrote:
> > 
> >>  - Add harvesting of slab allocator events. This needs to be checked for
> >>    weighing down the allocator code.
> > 
> > Hi,
> > 
> > Is this really doing it upon every one of those events? eg, for each
> > mbuf alloc through UMA?
> 
> Only if you turn it on!
> 
> M
> 

In random_harvestq_init() I see

 harvest_context.hc_source_mask = RANDOM_HARVEST_EVERYTHING_MASK;

and

#define RANDOM_HARVEST_EVERYTHING_MASK ((1 << (RANDOM_ENVIRONMENTAL_END
+ 1)) - 1)

So doesn't that include the RANDOM_FAST flag that controls harvesting
during every UMA alloc and free call?  And that harvesting appears to be
anything but fast, at least at a glance... it looks like it passes the
entire struct uma_zone to the jenkins hash function... is there really
useful entropy in all the data in that struct?

-- Ian