linux-kernel - Re: [PATCH RFC/RFB] x86_64, i386: interrupt dispatch changes

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: <491855AA.5060100@zytor.com>
Date:	Mon, 10 Nov 2008 07:39:22 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Alexander van Heukelum <heukelum@...tmail.fm>,
	Andi Kleen <andi@...stfloor.org>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Alexander van Heukelum <heukelum@...lshack.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>, lguest@...abs.org,
	jeremy@...source.com, Steven Rostedt <srostedt@...hat.com>,
	Mike Travis <travis@....com>
Subject: Re: [PATCH RFC/RFB] x86_64, i386: interrupt dispatch changes

Ingo Molnar wrote:
> * Alexander van Heukelum <heukelum@...tmail.fm> wrote:
> 
> hackbench is _way_ too noisy to measure such cycle-level differences 
> as irq entry changes cause. It also does not really stress interrupts 
> - it only stresses networking, the VFS and the scheduler.
> 
> a better test might have been to generate a ton of interrupts, but 
> even then it's _very_ hard to measure it properly. The best method is 
> what i've suggested to you early on: run a loop in user-space and 
> observe irq costs via RDTSC, as they happen. Then build a histogram 
> and compare the before/after histogram. Compare best-case results as 
> well (the first slot of the histogram), as those are statistically 
> much more significant than a noisy average.
> 

For what it's worth, I tested this out, and I'm pretty sure you need to
run a uniprocessor configuration (or system) for it to make sense --
otherwise you end up missing too many of the interrupts.  I first tested
this on an 8-processor system and, well, came up with nothing.

I'm going to try this later on a uniprocessor, unless Alexander beats me
to it.

	-hpa
--
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/