linux-kernel - Re: [ofa-general] Re: [GIT PULL] please pull ummunotify

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Message-ID: <20090929171332.GD14405@elf.ucw.cz>
Date:	Tue, 29 Sep 2009 19:13:32 +0200
From:	Pavel Machek <pavel@....cz>
To:	Roland Dreier <rdreier@...co.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, linux-rdma@...r.kernel.org,
	linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
	Anton Blanchard <anton@...ba.org>,
	general@...ts.openfabrics.org, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [ofa-general] Re: [GIT PULL] please pull ummunotify

On Thu 2009-09-17 08:45:29, Roland Dreier wrote:
> 
>  > > > Hmm, or are you saying you can only get 1 event per registered range and
>  > > > allocate the thing on registration? That'd need some registration limit
>  > > > to avoid DoS scenarios.
>  > > 
>  > > Yes, that's what I do.  You're right, I should add a limit... although
>  > > their are lots of ways for userspace to consume arbitrary amounts of
>  > > kernel resources already.
>  > 
>  > I'd be good to work at reducing that number, not adding to it ;-)
> 
> Yes, definitely.  I'll add a quick ummunotify module parameter that
> limits the number of registrations per process.
> 
>  > But yeah, I currently don't see a very nice match to perf counters.
> 
> OK.  It would be nice to tie into something more general, but I think I
> agree -- perf counters are missing the filtering and the "no lost
> events" that ummunotify does have.  And I'm not sure it's worth messing
> up the perf counters design just to jam one more not totally related
> thing in.

I believe that extending perf counters to do what you want is better
than adding one more, very strange, user<->kernel interface.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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