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From: Alex Elsayed <eternaleye@gmail.com>
Subject: Re: [PATCH 00/12] Add kdbus implementation
Date: Thu, 30 Oct 2014 13:28:09 -0700
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References: <1414620056-6675-1-git-send-email-gregkh@linuxfoundation.org> <alpine.LRH.2.00.1410292354480.11562@twin.jikos.cz> <20141029231106.GB16548@kroah.com> <alpine.LRH.2.00.1410300019570.11562@twin.jikos.cz> <20141029234001.GB16520@kroah.com> <CALCETrXY90YAXA9-GLc0EowmRCtWZzh8br8seiqrzOkmNn8_Hw@mail.gmail.com> <CAG-2HqX9RUQHiF1U_CXiDVVLS-7aUOQdYn7EVNSMZNdbe38cTA@mail.gmail.com> <CALCETrXv_CevG7166++ZHBok0ae7mNhF83VjrRVQ2AKF22Vf_g@mail.gmail.com>
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Andy Lutomirski wrote:

<snip>
> There should be a number measured in, say, nanoseconds in here
> somewhere.  The actual extent of the speedup is unmeasurable here.
> Also, it's worth reading at least one of Linus' many rants about
> zero-copy.  It's not an automatic win.

It's well-understood that it's not an automatic win; significant testing on 
multiple architectures indicated that 512K is a surprisingly universal 
crossover point. The userspace code, therefore, switches from copying 
(normal kdbus parameters) to zero-copy (memfds) right around there.

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