linux-kernel - Re: [RFC/HACK] x86: Fast return to kernel

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Message-ID: <20140504184016.GA16438@gmail.com>
Date:	Sun, 4 May 2014 20:40:16 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	"H. Peter Anvin" <h.peter.anvin@...el.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RFC/HACK] x86: Fast return to kernel


* Andy Lutomirski <luto@...capital.net> wrote:

> > That said, regular *device* interrupts do often return to kernel 
> > mode (the idle loop in particular), so if you have any way to 
> > measure that, that might be interesting, and might show some of 
> > the same advantages.
> 
> I can try something awful involving measuring latency of 
> hardware-timed packets on a SolarFlare card, but I'll have 
> calibration issues.  I suppose I could see if 'ping' gets faster.  
> In general, this will speed up interrupts that wake userspace from 
> idle by about 100ns on my box, since it's presumably the same size 
> and the speedup per loop in my silly benchmark.

To simulate high rate device IRQ you can generate very high frequency 
lapic IRQs by using hrtimers, that's generating a ton of per CPU lapic 
IRQs.

Thanks,

	Ingo
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