svn commit: r275136 - in head/sys: dev/e1000 dev/ixgbe kern sys
John Baldwin
jhb at freebsd.org
Mon Dec 1 15:49:22 UTC 2014
On Monday, December 01, 2014 07:19:13 AM Alfred Perlstein wrote:
> John,
>
> Will work on a new revision based on feedback.
>
> Two things to note however:
>
> Already explored the idea of using kernel_sysctlbyname but rejected due to
> following:
>
> It makes little sense to have a rw sysctl that only takes effect "some
> times". This violates POLA at the expense of making code appear cleaner.
> Expectation is that writable sysctls take effect or are read only. They are
> not to be "write sometimes" unless we are to introduce a new flag. Instead
> of going to a confusing model we consider some form of rw sysctl that can
> set itself ro somehow. Otherwise people will be confused as to why nic
> queues says N while actually M. What the rw->ro api would look like I have
> no idea. Suggestions?
This is only somewhat true. In the near distant future we will have a devctl
tool which would let you do 'devctl detach igb0 && devctl attach igb0' which
would honor your post-boot setting of hw.igb.num_queues. Instead what is
important to understand about this particular sysctl node is that it only
takes affect when a device is attached. However, there are other control
knobs that also only affect future operations and not existing instances of
objects, so I don't think this is that big of a leap.
--
John Baldwin
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