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Date:      Fri, 20 May 2005 11:37:38 -0700
From:      Kris Kennaway <kris@obsecurity.org>
To:        Gleb Smirnoff <glebius@FreeBSD.org>
Cc:        Jeremie Le Hen <jeremie@le-hen.org>
Subject:   Re: panic in recent RELENG_5 tcp code path
Message-ID:  <20050520183738.GA53549@xor.obsecurity.org>
In-Reply-To: <20050520131536.GA30219@cell.sick.ru>
References:  <20050515120007.GA777@obiwan.tataz.chchile.org> <20050518155130.H87264@carver.gumbysoft.com> <20050519125639.GK818@obiwan.tataz.chchile.org> <20050520080435.GB26938@cell.sick.ru> <20050520131031.GU818@obiwan.tataz.chchile.org> <20050520131536.GA30219@cell.sick.ru>

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On Fri, May 20, 2005 at 05:15:36PM +0400, Gleb Smirnoff wrote:
>   Jeremie,
>=20
> On Fri, May 20, 2005 at 03:10:32PM +0200, Jeremie Le Hen wrote:
> J> > according to the fact that the panic occured in dereferncing mbuf po=
inter
> J> > your kernel is compiled without INVARIANTS.
> J> >=20
> J> > Please compile it with INVARIANTS. This will probably help to trigge=
r panic
> J> > earlier, and it will be more clear.
> J>=20
> J> a quick look at src/conf/NOTES reveals the following :
> J> %%%
> J>     #
> J>     # The INVARIANTS option is used in a number of source files to ena=
ble
> J>     # extra sanity checking of internal structures.  This support is n=
ot
> J>     # enabled by default because of the extra time it would take to ch=
eck
> J>     # for these conditions, which can only occur as a result of
> J>     # programming errors.
> J>     #
> J> %%%
> J>=20
> J> I'm going to recompile my kernel with INVARIANTS but I wonder in
> J> which order of magniture it will slow my kernel down.  In other words,
> J> what does INVARIANTS do concretely, shall I expect a performance drop
> J> like WITNESS does ?
>=20
> No. The performance loss is _much_ less significant than in WITNESS case.
> You probably will not notice it.

Actually, INVARIANTS causes about a 10% penalty on wall clock time on
5.x and above.

Kris
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