Date: Fri, 17 Feb 2012 16:36:30 -0800 From: Julian Elischer <julian@freebsd.org> To: Marcel Moolenaar <marcel@xcllnt.net> Cc: marcel@freebsd.org, Eitan Adler <eadler@freebsd.org>, svn-src-all@freebsd.org, "Kenneth D. Merry" <ken@freebsd.org>, Andriy Gapon <avg@freebsd.org>, src-committers@freebsd.org, Bruce Evans <brde@optusnet.com.au>, svn-src-head@freebsd.org Subject: Re: svn commit: r231814 - in head/sys: kern sys Message-ID: <4F3EF28E.5030004@freebsd.org> In-Reply-To: <B0FF5A36-FE36-4734-950C-2BB21318161D@xcllnt.net> References: <201202160511.q1G5BZNk099785@svn.freebsd.org> <20120216181210.K1423@besplex.bde.org> <4F3CC40D.4000307@freebsd.org> <4F3CC5C4.7020501@FreeBSD.org> <4F3CC8A5.3030107@FreeBSD.org> <20120216174758.GA64180@nargothrond.kdm.org> <20120217053341.R1256@besplex.bde.org> <20120217000846.GA7641@nargothrond.kdm.org> <4F3D9D03.6020507@FreeBSD.org> <9CB7ECE8-FF10-43BE-9EBD-16953BE3B193@xcllnt.net> <4F3E0596.6040808@freebsd.org> <B0FF5A36-FE36-4734-950C-2BB21318161D@xcllnt.net>
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> On Feb 16, 2012, at 11:45 PM, Julian Elischer wrote:
> *snip*
>>> The message buffer does not have to be a chunk of memory that
>>> we circularly scribble to. It can be a per-cpu linked list of
>>> messages even.
> *snip*
>
>> that is an intersting thought.. though.. how would you sort them into order for
>> printing?
>>
>> maybe a single atomic 64 bit int that is incremented per message.
> Yes. Though, a timestamp should do the trick as well. In a multi-core
> system, you won't have pure or absolute sequentially anymore. For
> messages that are "printed" at the proverbial "same time" on different
> cores, ordering is very hard, if not impossible, to determine. A single
> atomic counter would force sequentially, but would effectively introduce
> serialization, just like locking, and would make a per-cpu message
> buffer/list/whatever less useful.
bit a single atomic op, while expensive would be within the cost I
could live with.
> The theory: the closer in time independent messages are printed (on
> different cores), the least important their ordering becomes.
not necessarily. sometimes teh order is important to find the problem..
("look, it read it before the other one wrote it").
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