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Date:      Tue, 7 Apr 2009 10:24:44 +0100 (BST)
From:      Robert Watson <rwatson@FreeBSD.org>
To:        Sepherosa Ziehau <sepherosa@gmail.com>
Cc:        freebsd-net@freebsd.org, Ivan Voras <ivoras@freebsd.org>
Subject:   Re: Advice on a multithreaded netisr patch?
Message-ID:  <alpine.BSF.2.00.0904071024070.45341@fledge.watson.org>
In-Reply-To: <ea7b9c170904062209tda44636tb9a18755ec0c5bb3@mail.gmail.com>
References:  <gra7mq$ei8$1@ger.gmane.org> <alpine.BSF.2.00.0904051422280.12639@fledge.watson.org> <grac1s$p56$1@ger.gmane.org> <alpine.BSF.2.00.0904051440460.12639@fledge.watson.org> <grappq$tsg$1@ger.gmane.org> <alpine.BSF.2.00.0904052243250.34905@fledge.watson.org> <grbcfg$poe$1@ger.gmane.org> <alpine.BSF.2.00.0904061238250.34905@fledge.watson.org> <ea7b9c170904062209tda44636tb9a18755ec0c5bb3@mail.gmail.com>

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On Tue, 7 Apr 2009, Sepherosa Ziehau wrote:

>> This issue is almost entirely independent from things like the cache line 
>> miss issue, unless you hit the uncommon case of having to do work in 
>> m_pullup(), in which case life sucks.
>>
>> It would be useful to use DTrace to profile a number of the workfull 
>> m_foo() functions to make sure we're not hitting them in normal workloads, 
>> btw.
>
> I highly suspect m_pullup will take any real effect on RX path, given how 
> most of drivers allocate the mbuf for RX ring (all RX mbufs should be 
> mclusters).

Agreed, but it's good to be sure one is right about these things. :-)

Robert N M Watson
Computer Laboratory
University of Cambridge



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