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From: John Kacur <jkacur@redhat.com>
To: Tracy Smith <tlsmith3777@gmail.com>
Cc: Piotr Gregor <piotrgregor@rsyncme.org>,
	Clark Williams <williams@redhat.com>,
	Linux RT Users <linux-rt-users@vger.kernel.org>
Subject: Re: Calculate average latencies on the fly
Date: Tue, 22 Nov 2016 10:43:27 -0500 (EST)	[thread overview]
Message-ID: <477381688.1371680.1479829407972.JavaMail.zimbra@redhat.com> (raw)
In-Reply-To: <CAChUvXOj_D2N3o7BoEUjt1A1O0fXZnvGSz5ba=O55h12ns___A@mail.gmail.com>



----- Original Message -----
> John,
> 
> Latency of 100,000 seems to me to be a bug when doing floating point long
> division, which potentially accumulates small errors.
> 
> Is the issue in the cyclictest calculation or in the kernel?  Or, the FPU?
> 
> If in the kernel, where do we need to trace to check for increased latency
> when doing floating point long division?
> 
> Piotr, needs to trace where the latency is occurring and fix.  Any
> recommendations on a possible fix at this stage?
> 
> Thx, Tracy
> 

Sure, you make some good points, it could be a cyclictest bug, it could be in the kernel, 
he also said he was doing this in a virtualized system, it could be somewhere in that stack.
The first step of course is to see if you can come up with a way to reliably reproduce it.

Thanks

John

      parent reply	other threads:[~2016-11-22 15:43 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-11-14 10:00 Calculate average latencies on the fly Piotr Gregor
2016-11-14 11:50 ` Piotr Gregor
2016-11-14 15:42   ` Mathieu Poirier
2016-11-14 16:11     ` Piotr Gregor
2016-11-14 16:58       ` Clark Williams
2016-11-16 14:47   ` John Kacur
2016-11-19 23:27     ` Piotr Gregor
2016-11-20  5:03       ` Tracy Smith
2016-11-21 18:32       ` John Kacur
     [not found]         ` <CAChUvXOj_D2N3o7BoEUjt1A1O0fXZnvGSz5ba=O55h12ns___A@mail.gmail.com>
2016-11-22 15:43           ` John Kacur [this message]

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