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Date:      Mon, 30 Nov 2020 12:48:47 -0800
From:      David Wolfskill <david@catwhisker.org>
To:        current@freebsd.org
Subject:   Re: Laptop exhibits erratic responsiveness
Message-ID:  <X8Var0P/N8TDLOMA@albert.catwhisker.org>
In-Reply-To: <X8Tx2LBXpRihqqfh@albert.catwhisker.org>
References:  <X8JVn/PIPuLzsWuQ@albert.catwhisker.org> <CADrOrms8fmf9asttPw%2B4B%2BKL7A4svAKx0dDHSuDnEVvxGWiX0Q@mail.gmail.com> <X8OsLaVToS1V1zoX@albert.catwhisker.org> <CAGudoHHevDxuvwLO2QMrMNfvG0vWSU=v9gHLbH0eMFDt8p0FWg@mail.gmail.com> <X8Tpg1P%2BXQc7iTNJ@albert.catwhisker.org> <CAGudoHEZvoj5s2bOz_atg9oPQM=24i5ydGZVebuLQAu0nbS0TA@mail.gmail.com> <X8Tx2LBXpRihqqfh@albert.catwhisker.org>

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On Mon, Nov 30, 2020 at 05:21:28AM -0800, David Wolfskill wrote:
> ...
> FWIW, the copy of the laptop's "head" kernel config in
> http://www.catwhisker.org/~david/FreeBSD/head/CANARY is current.
>=20
> And the only difference between the stable/12 config and the head config
> is:
>=20
> g1-48(12.2-S)[3] diff -u FreeBSD-1{2,3}/CANARY
> --- FreeBSD-12/CANARY   2019-07-08 10:43:51.940026000 -0700
> +++ FreeBSD-13/CANARY   2015-03-22 10:03:41.000000000 -0700
> @@ -342,7 +342,7 @@
>  # from some parts of the kernel.  As this makes everything more noisy,
>  # it is disabled by default.
>  #
> -# options      DIAGNOSTIC
> +options        DIAGNOSTIC
> =20
>  #
>  # REGRESSION causes optional kernel interfaces necessary only for regres=
sion
>=20
> Hmmm... so I suppose that re-disbling DIAGNOSTIC might be a reasonable
> thing to try, as well, yeah...?  :-}
> ....

Well, success(ish):

* I was able to reproduce the observed effect using the newer laptop,
running a kernel from 14 Nov (thus, r367674):

* I was able to reproduce the observed effect using the newer laptop,
  running a kernel from 14 Nov (thus, r367674).  (I had cloned the old
  laptop's disk drive and slapped it inito the newer laptop.)

* I then updated the kernel config file ("CANARY") to comment out the
  DIAGNOSTIC option, then rebuilt/installed the kernel.

* Upon reboot, "ping albert" showed remarkably consistent RTTs (compared
  to before) -- e.g., the initial example I posted showed:

  --- albert.catwhisker.org ping statistics ---
  67 packets transmitted, 67 packets received, 0.0% packet loss
  round-trip min/avg/max/stddev =3D3D 0.428/1024.248/68482.244/8303.513 ms

  On the newer laptop after the above change, I saw:

  --- albert.catwhisker.org ping statistics ---
  30 packets transmitted, 30 packets received, 0.0% packet loss
  round-trip min/avg/max/stddev =3D 0.463/0.574/0.671/0.054 ms

Please especially note the maxima & standard deviations.


FWIW, I do have (in /boot/loader.conf):

# Try to reduce WITNESS overhead
vm.debug.divisor=3D4

(which I also utilize at work).

I suppose I will be commenting out that DIAGNOSTIC option now.... :-}

Peace,
david
--=20
David H. Wolfskill                              david@catwhisker.org
There's no point in asking Trump "Sir, have you no decency?" -- it is
already well established that neither he nor his enablers have any.

See http://www.catwhisker.org/~david/publickey.gpg for my public key.

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