linux-kernel - Re: [bisected] pty performance problem

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Message-ID: <20091121231514.3012e679@infradead.org>
Date:	Sat, 21 Nov 2009 23:15:14 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Robert Swan <swan.r.l@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: [bisected] pty performance problem

On Sun, 22 Nov 2009 07:39:26 +0100
Ingo Molnar <mingo@...e.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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