Date: Fri, 8 May 2009 20:13:32 -0400 From: jt@0xabadba.be To: Ed Schouten <ed@80386.nl> Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org>, vasanth raonaik <vasanth.raonaik@gmail.com> Subject: Re: concurrent sysctl implementation Message-ID: <3C2B6A87-C127-4E1F-9A1E-DADF613B18BF@0xabadba.be> In-Reply-To: <20090508214117.GY58540@hoeg.nl> References: <a0806f900905050107u4cbf0624oc83aafa54ae651f0@mail.gmail.com> <d9f479c10905050239u5d6d8304y1f63e41eabee8624@mail.gmail.com> <20090508214117.GY58540@hoeg.nl>
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Ed,
Thanks :) I'll be implementing this as discussed over the next few
months thanks for the technical detail I've been extremely busy with
finals. I will write the list with my thoughts within the next week,
sorry for the delay.
=jt
On May 8, 2009, at 17:41, Ed Schouten <ed@80386.nl> wrote:
> Hi,
>
> * vasanth raonaik <vasanth.raonaik@gmail.com> wrote:
>> Hello Jt,
>>
>> I am a newbee in this alias. I am having a very basic question. It
>> would be
>> really good if you could give me some of this information.
>> Could you please elaborate on what is the current architecture of
>> sysctl
>> implementation and How the concurrency would benefit us.
>
> Right now sysctl is synchronized using the sysctl lock. The problem is
> that certain sysctls just block for a very long time (especially
> some of
> the GEOM ones). We also call sysctl when we execute new processes, to
> obtain a random number for the stack protector. This means we have
> quite
> a lot of contention on it. This lock needs to be there, because
> sysctls
> can be added and removed on demand.
>
> I think I discussed this with John Baldwin (right?) and I think we
> also
> have the issue that we cannot allow an unbounded amount of concurrent
> calls to sysctl, because sysctl wires memory.
>
> A solution would be to solve it as follows:
>
> - Use a semaphore, initialized to some insane high value to put an
> upper
> limit on the amount of concurrent sysctl calls. I'm not sure whether
> this is really needed. Maybe this issue is not as serious as we think
> it is.
>
> - Use an rw/rm/sxlock to protect the sysctl tree, but only pick up
> the lock when we traverse parts of the sysctl tree that has
> dynamically created entries.
>
> --
> Ed Schouten <ed@80386.nl>
> WWW: http://80386.nl/
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