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

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Message-ID: <ada63b0tl9j.fsf@cisco.com>
Date:	Wed, 30 Sep 2009 10:06:32 -0700
From:	Roland Dreier <rdreier@...co.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Pavel Machek <pavel@....cz>, 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
Subject: Re: [ofa-general] Re: [GIT PULL] please pull ummunotify


 > 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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