Date: Sat, 21 Nov 2009 23:15:14 -0800
From: Arjan van de Ven <arjan@infradead.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Robert Swan <swan.r.l@gmail.com>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>, linux-kernel@vger.kernel.org
Subject: Re: [bisected] pty performance problem
Message-ID: <20091121231514.3012e679@infradead.org>
In-Reply-To: <20091122063926.GA18224@elte.hu>
References: <20091121222319.GA3905@swanrl.gmail.com>
	<20091122063926.GA18224@elte.hu>
Organization: Intel
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On Sun, 22 Nov 2009 07:39:26 +0100
Ingo Molnar <mingo@elte.hu> wrote:
> > ! Neither has any I/O apart from the pty conversation, so I'd
> > expect to ! see CPU usage at 100%. When I ran it, the CPU was
> > pretty well idle. ! After a fair bit of fiddling, it turned out
> > that both sides were ! taking about 8ms for their read() calls. At
> > that point it seemed ! pretty clear that this was a delay in the
> > kernel, not the code. ! 
> > [snip]
> > 
> > I can provide reasonably stripped down code which demonstrates the
> > problem.  It has been reproduced by one other person, though his
> > delay was about 2ms.


let me guess; you have HZ=250 and the other person has HZ=1000...
since this seems consistent with doing a 1 jiffy delay...


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
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