Message-Id: <200605010702.k4172Q5H006348@turing-police.cc.vt.edu>
To: Circuitsoft Development <circuitsoft.devel@gmail.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Extended Volume Manager API 
In-Reply-To: Your message of "Mon, 01 May 2006 00:26:05 CDT."
             <64b292120604302226i377f1c37qd33db36693ea1871@mail.gmail.com> 
From: Valdis.Kletnieks@vt.edu
References: <64b292120604302226i377f1c37qd33db36693ea1871@mail.gmail.com>
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On Mon, 01 May 2006 00:26:05 CDT, Circuitsoft Development said:

> Having done my own tests, I've determined that a 5msec timeout to
> determine if a host has crashed would be appropriate. (My test was
> basically looking at ping time over a saturated network - averaged
> about 600 microseconds, topped at 3msec over 10 minutes) I figure that
> 5msec timeout won't add any noticeable lag to the volume manager, as
> most disk seek times are in that range.W

Note that if you're setting 5ms as your timeout for detecting a *crash*,
and your *ping* takes 3ms, that leaves you a whole whopping 2ms.  If you
have 1ms scheduler latency at *each* end (remember - you're in userspace
at both ends, right?) you have approximately 0ms left for the remote end to
actually *do* anything, and for the local end to process the reply.

And if the remote end has to issue a syscall during processing the request,
you're basically screwed.

You need to be adding at least 1 zero to that timeout value.

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