linux-kernel - Re: [RFC][PATCH 3/3] perf_counter: new output ABI

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <18884.46934.898678.53966@cargo.ozlabs.ibm.com>
Date:	Sat, 21 Mar 2009 20:45:58 +1100
From:	Paul Mackerras <paulus@...ba.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 3/3] perf_counter: new output ABI - part 1

Ingo Molnar writes:

> i think it would still be nice to allow plain old-fashioned 
> poll()+read() loops ... but the logistics of that seem difficult. 
> mmap() seems to fit this better - and it's probably faster as well. 
> (as we have to construct the kernel-space pages anyway, so mapping 
> them isnt that big of an issue)
> 
> per-CPU-ness will be handled naturally via per-cpu counters.
> 
> Paul, can you see any hole/quirkiness in this scheme?

The one thing I can see that we would lose is the ability to have a
signal delivered on every event.  The PAPI developers want to be able
to get a signal generated every time the counter overflows, and
previously we could do that using the O_ASYNC flag, but now we'll only
get a signal every page's worth of events.

So I think we want userspace to be able to say how often we should
generate a poll event, i.e. provide a way for userspace to say "please
generate a poll event every N counter events".  That would also solve
the problem of 1 page not being a valid configuration - you could set
the poll interval to the number of events that fit in half a page, for
instance.

Paul.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/