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Re: Route cache performance under stress

To: "David S. Miller" <davem@xxxxxxxxxx>
Subject: Re: Route cache performance under stress
From: Ralph Doncaster <ralph@xxxxxxxxx>
Date: Tue, 10 Jun 2003 20:41:13 -0400 (EDT)
Cc: "Robert.Olsson@xxxxxxxxxxx" <Robert.Olsson@xxxxxxxxxxx>, "hadi@xxxxxxxxxxxxxxxx" <hadi@xxxxxxxxxxxxxxxx>, "xerox@xxxxxxxxxx" <xerox@xxxxxxxxxx>, "sim@xxxxxxxxxxxxx" <sim@xxxxxxxxxxxxx>, "fw@xxxxxxxxxxxxx" <fw@xxxxxxxxxxxxx>, "netdev@xxxxxxxxxxx" <netdev@xxxxxxxxxxx>, "linux-net@xxxxxxxxxxxxxxx" <linux-net@xxxxxxxxxxxxxxx>
In-reply-to: <20030610.165759.78731321.davem@xxxxxxxxxx>
References: <Pine.LNX.4.51.0306101725020.17226@xxxxxxxxxxxx> <20030610.152020.59678979.davem@xxxxxxxxxx> <Pine.LNX.4.51.0306101956520.7801@xxxxxxxxxxxx> <20030610.165759.78731321.davem@xxxxxxxxxx>
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On Tue, 10 Jun 2003, David S. Miller wrote:

>    From: Ralph Doncaster <ralph@xxxxxxxxx>
>    Date: Tue, 10 Jun 2003 19:58:47 -0400 (EDT)
>
>    On Tue, 10 Jun 2003, David S. Miller wrote:
>
>    > Every packet records a timestamp.
>
>    I'm not aware of anything in IP routing that requires a timestamp for
>    every packet.  To me it sounds like we could rip that out too.
>
> Guess you never run tcpdump nor use packet schedulers.

So because some (in the case of a core router almost none) of the packets
will need a timestamp, you do it for every single one of them?

This sounded so unbelievable to me that I took a quick look at the code to
see what I'd have to do to get rid of it.  It appears that gettimeofday is
not called for every packet; just for ICMP timestamp requests and for IP
options (ip_options_build and ip_options_compile).

-Ralph

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