Date: Mon, 1 Dec 2014 07:55:57 -0800 From: Alfred Perlstein <bright@mu.org> To: John Baldwin <jhb@freebsd.org> Cc: "svn-src-head@freebsd.org" <svn-src-head@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, Alfred Perlstein <alfred@freebsd.org>, "src-committers@freebsd.org" <src-committers@freebsd.org> Subject: Re: svn commit: r275136 - in head/sys: dev/e1000 dev/ixgbe kern sys Message-ID: <6753416A-D6FD-47F4-A62E-99A6ABB9B4B2@mu.org> In-Reply-To: <1762770.yx1cv63jp7@ralph.baldwin.cx> References: <201411262019.sAQKJaw4043557@svn.freebsd.org> <39377603.10OyiSzjWY@ralph.baldwin.cx> <872C180A-6ADD-469F-A801-3728DF134EEC@mu.org> <1762770.yx1cv63jp7@ralph.baldwin.cx>
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> On Dec 1, 2014, at 7:49 AM, John Baldwin <jhb@freebsd.org> wrote: > >> 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. > Strongly disagree here. If I were not able to grok the c code I would be very confused by such a thing. In fact even with the fact that I do grok c code I would be very discouraged to find such behavior and strongly object to writable sysctls that do nothing. The ux is that the user has a bunch of dials on their dashboard that function as a busybox as opposed to doing what they are advertised to do. Sort of like those crossing light buttons in New York City that aren't actually hooked to anything. So: No. Frankly would rather back out the change entirely and keep this change local to us than expose users to such a UX. I will however like to discuss the possibility of a tunable/sysctl system that makes sense. -Alfred. > -- > John Baldwin >home | help
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