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Date:      Sun, 22 Sep 2013 22:34:24 -0700
From:      Adrian Chadd <adrian@freebsd.org>
To:        Luigi Rizzo <rizzo@iet.unipi.it>
Cc:        "Alexander V. Chernikov" <melifaro@yandex-team.ru>, Luigi Rizzo <luigi@freebsd.org>, Andre Oppermann <andre@freebsd.org>, "Andrey V. Elsukov" <ae@freebsd.org>, FreeBSD Net <net@freebsd.org>
Subject:   Re: Network stack changes
Message-ID:  <CAJ-Vmokv-q-zRhbYF6mmdHAhuyqS-f8hxhPBXcZmwVLCYj1kJw@mail.gmail.com>
In-Reply-To: <CA%2BhQ2%2BirPxdBW%2BHScbnXi3p134HC2pnPSPMj=UAmHDGY_dV7PA@mail.gmail.com>
References:  <521E41CB.30700@yandex-team.ru> <CAJ-Vmo=N=HnZVCD41ZmDg2GwNnoa-tD0J0QLH80x=f7KA5d%2BUg@mail.gmail.com> <523F4F14.9090404@yandex-team.ru> <CAJ-VmokmaVds-DVj6yYAWSSwg=RBYJLeFfg8ae-Oj3_bOdcRyA@mail.gmail.com> <CA%2BhQ2%2BirPxdBW%2BHScbnXi3p134HC2pnPSPMj=UAmHDGY_dV7PA@mail.gmail.com>

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On 22 September 2013 21:52, Luigi Rizzo <rizzo@iet.unipi.it> wrote:


> locking affects scalability; but dxr and similar algorithms have much fewer
> memory lookups, not to mention the huge memory footprint of
> the freebsd radix tree code.
>
> Anyways i'd really encourage you to read the dxr paper, it is short
> and hopefully can give you a better idea of the details (and with data
> supporting them) than these short notes.
>
>
I read the paper. :-)

I believe it! It's not the first paper that I've read that packed a FIB
into a sensibly cacheable structure. I'm just as interested however in
making sure that we actually give people the tools to inspect this stuff
for themselves, rather than all of us hacking up something from scratch
every time we want to profile this kind of thing.

The other side of this coin is locking, and the paper didn't go into that.
Eliminating the radix tree overhead is great; now we just have to avoid
grabbing all those locks all the damned time for each frame..



-adrian



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