From owner-svn-src-all@freebsd.org  Wed Oct 12 09:44:06 2016
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Date: Wed, 12 Oct 2016 12:44:03 +0300
From: Slawa Olhovchenkov <slw@zxy.spb.ru>
To: "Jonathan T. Looney" <jtl@FreeBSD.org>
Cc: src-committers@freebsd.org, svn-src-all@freebsd.org,
 svn-src-head@freebsd.org
Subject: Re: svn commit: r307082 - in head: . sys/amd64/conf sys/arm/conf
 sys/arm64/conf sys/conf sys/i386/conf sys/mips/conf sys/modules/cc
 sys/modules/khelp sys/netinet sys/netinet/tcp_stacks sys/pc98/conf sy...
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On Wed, Oct 12, 2016 at 02:16:42AM +0000, Jonathan T. Looney wrote:

> Author: jtl
> Date: Wed Oct 12 02:16:42 2016
> New Revision: 307082
> URL: https://svnweb.freebsd.org/changeset/base/307082
> 
> Log:
>   In the TCP stack, the hhook(9) framework provides hooks for kernel modules
>   to add actions that run when a TCP frame is sent or received on a TCP
>   session in the ESTABLISHED state. In the base tree, this functionality is
>   only used for the h_ertt module, which is used by the cc_cdg, cc_chd, cc_hd,
>   and cc_vegas congestion control modules.
>   
>   Presently, we incur overhead to check for hooks each time a TCP frame is
>   sent or received on an ESTABLISHED TCP session.

Do you perform estimate of performane impact of this overhead?