From: Sankara Muthukrishnan <sankara.m@gmail.com>
To: Mike Galbraith <efault@gmx.de>
Cc: "Raphaël Beamonte" <raphael.beamonte@gmail.com>,
linux-rt-users@vger.kernel.org
Subject: Re: Latency problem
Date: Tue, 1 Nov 2011 16:24:20 -0500 [thread overview]
Message-ID: <CAFQPvXch7YqaRdhtzhf5j1vLsGEGFhZc7idA0aWrcfCdotz3kg@mail.gmail.com> (raw)
In-Reply-To: <1319777643.6150.7.camel@marge.simson.net>
2011/10/27 Mike Galbraith <efault@gmx.de>:
> On Thu, 2011-10-27 at 15:03 -0400, Raphaël Beamonte wrote:
>
>> Moreover, the use of hwlatdetect seems to confirm that the problem is
>> from hardware.
>
> Yeah, skimmed over your message too quick, thinking nsecs instead of
> usecs. Probably SMIs.
>
> -Mike
>
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>
One way to find out whether the spikes in the latency are due to
SMI(System Management Interrupt) is to read the MSR register that
keeps the count of SMIs. So, read the MSR in the start of the test
program and the end of the test and see whether the count has
increased. Unfortunately, it is model-specific-register and I am not
sure whether AMD supports it. I don't think all Intel processors
support it either. I know that Nehalem based Intel Core-i7 arrandale
processor supports counting SMI thru MSR 0x34 and I have not found it
documented in any Intel documentation but found in some reference BIOS
source. I have tested it with legacy USB interrupts and found it to
work. RDMSR is a privilege-0 instruction though.
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next prev parent reply other threads:[~2011-11-01 21:24 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-27 16:03 Latency problem Raphaël Beamonte
[not found] ` <1319741477.6197.26.camel@marge.simson.net>
2011-10-27 19:03 ` Raphaël Beamonte
2011-10-28 4:54 ` Mike Galbraith
2011-11-01 21:24 ` Sankara Muthukrishnan [this message]
[not found] ` <CAE_Gge2hbE0Shg4NrNvYswCDHhgAEwZsSUACuM5Tsmt8CqCP=g@mail.gmail.com>
2011-11-01 22:12 ` Raphaël Beamonte
[not found] ` <CAFQPvXcyLpisRJ11=-5w7tSwN+A+oKYc_ExGCYSZxMov1-zHxg@mail.gmail.com>
2011-11-02 16:28 ` Sankara Muthukrishnan
2011-10-27 21:15 ` Carsten Emde
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