From: Roland Dreier <rdreier@cisco.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Pavel Machek <pavel@ucw.cz>, Peter Zijlstra <peterz@infradead.org>,
       linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org,
       Paul Mackerras <paulus@samba.org>, Anton Blanchard <anton@samba.org>,
       general@lists.openfabrics.org, akpm@linux-foundation.org,
       torvalds@linux-foundation.org
Subject: Re: [ofa-general] Re: [GIT PULL] please pull ummunotify
References: <aday6omhz9d.fsf@cisco.com> <1253187028.8439.2.camel@twins>
	<adafxalejiq.fsf@cisco.com> <adaab0tej5c.fsf@cisco.com>
	<1253198976.14935.27.camel@laptop> <adazl8td35u.fsf@cisco.com>
	<adatyz1d17q.fsf@cisco.com> <20090929171332.GD14405@elf.ucw.cz>
	<20090930094456.GD24621@elte.hu>
Date: Wed, 30 Sep 2009 10:06:32 -0700
In-Reply-To: <20090930094456.GD24621@elte.hu> (Ingo Molnar's message of "Wed,
	30 Sep 2009 11:44:56 +0200")
Message-ID: <ada63b0tl9j.fsf@cisco.com>
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 > Performance events filtering is being worked on and now with the proper 
 > non-DoS limit you've added you can lose events too, dont you? So it's 
 > all a question of how much buffering to add - and with perf events too 
 > you can buffer arbitrary large amount of events.

No, the idea for non-DoS for ummunotify is that we would limit the
number of regions the application can register; so an application might
hit the limit up front but no runtime loss of events once a region was
registered successfully.

 > I think this could be done in a simpler, less limited, more generic, 
 > more useful form by using some variation of perf events.
 > 
 > You should be able to get all that you want by adding two TRACE_EVENT() 
 > tracepoints and using the existing perf event syscall to get the events 
 > to user-space.

Yes, I would like to use perf events too.  Would it be plausible to
create a way for userspace to create a "counter" for each address range
being watched?  Then events would not be lost, because those counters
would become non-zero.

 > Meaning that this:
 >   9 files changed, 1060 insertions(+), 1 deletions(-)

Note that lots/ of the files touched here are in Documentation or are
one-line changes to Makefiles etc.

 - R.
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