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: <20090115112100.GC22850@elte.hu>
Date:	Thu, 15 Jan 2009 12:21:00 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH] perf_counter: Add support for pinned and exclusive
	counter groups


* Paul Mackerras <paulus@...ba.org> wrote:

> Ingo Molnar writes:
> 
> > (btw., the percpu allocation code seems to have bitrotten a bit - the 
> > logic around perf_reserved_percpu looks wrong and somewhat complicated.)
> 
> Yes, it has.  I don't think it was ever fixed to apply only to hardware 
> counters when software counters were added.
> 
> Side question - were you intending to make the various software counters 
> able to act as interrupting counters?  That will mean e.g. that anything 
> that increments current->maj_flt or current->min_flt (i.e. 
> do_page_fault, __get_user_pages) will need to check if that causes any 
> counter to overflow, which could be a bit invasive.

Yes, eventually my intention was to bring all the sw counters up to that 
level, and allow system sampling via sw counter overflows. It's an 
arguably powerful concept.

I first wanted to see where they all go though, and how many of them we 
want, and how nuanced we want to make them.

Initially we can sample via __builtin_return_address(0) addresses, or 
pt_regs(current)->rip or so. Later on we could use save_stack_trace() 
perhaps, for a more vectored sample.

It would result in some rather cool kerneltop output: we could see a 
profile of which functions generate pagefaults, or which places generate 
context-switches, which places migrate a lot, etc.

> > Again, which restrictions users/developers are more willing to live 
> > with will be shown in actual usage of these facilities.
> 
> Indeed.

So my approach was always to have a good guess about what the best usage 
pattern is, but also to not be rigid and ignore/exclude other usecases. 
The main principle of this subsystem is to be maximally useful in 
performance analysis, via modern and flexible abstractions. Pinning and 
exclusivity fits into that just fine - they are mechanism to improve the 
quality of the statistics.

	Ingo
--
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/

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ