linux-kernel - Re: [patch 0/3] kvm tool: Serial emulation overhaul

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Date:	Mon, 12 Dec 2011 20:31:38 +0200
From:	Pekka Enberg <penberg@...nel.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Sasha Levin <levinsasha928@...il.com>
Subject: Re: [patch 0/3] kvm tool: Serial emulation overhaul

On Mon, 2011-12-12 at 20:19 +0200, Avi Kivity wrote:
> On 12/12/2011 01:19 PM, Pekka Enberg wrote:
> > On Sun, Dec 11, 2011 at 5:53 PM, Ingo Molnar <mingo@...e.hu> wrote:
> > > Okay, but look at it from another angle: the top output i
> > > generate is about 300k characters. 5000 msecs to execute it
> > > means 16 usecs overhead per character - or about 50k cycles - on
> > > a top of the class x86 CPU.
> >
> > I'm seeing 1.5 usecs per character for this little benchmark:
> 
> No interrupts, right?  Things look differently with one interrupt per
> character and none. 

No interrupts. I was simply trying to measure PIO overhead to see how
bad the 15 usec per character Ingo measured really is.

			Pekka

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