linux-kernel - Re: Regression: kernels since 2.6.26 are unusably slow

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Message-ID: <501db8660909251802hacbaf04wb8dc1734fa523d34@mail.gmail.com>
Date:	Sat, 26 Sep 2009 02:02:03 +0100
From:	Aneurin Price <aneurin.price@...il.com>
To:	Frans Pop <elendil@...net.nl>
Cc:	linux-kernel@...r.kernel.org, Yinghai Lu <yinghai.lu@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Regression: kernels since 2.6.26 are unusably slow

On Fri, Sep 25, 2009 at 23:51, Frans Pop <elendil@...net.nl> wrote:
> Adding maintainers involved with the commit in CC.
>
> Aneurin Price wrote:
>> Hi,
>> Every kernel since 2.6.26 has been unusably slow for me - to the extent
>> that I initially thought they were hanging on boot. Exactly how bad it is
>> seems to vary, but it could take several minutes to boot, and then
>> another minute or two to log in (with bash pegging the CPU as it loads).
>> Everything seems to need vastly more CPU time than usual - it feels a
>> little like I'm using a 486.
>>
>> I've bisected the problem down to commit
>> 42651f15824d003e8357693ab72c4dbb3e280836 (x86: fix trimming e820 with
>> MTRR holes). Having basically no idea what that means, I thought I'd try
>> building a kernel with MTRRs disabled, to see if that would make any
>> difference, but no joy.
>>
>> Can anyone give me some idea of where to go next, or let me know what
>> further information I should provide?
>
> Let's start with some basic info. Can you please send your kernel config
> and the output of 'dmesg' after a boot with a "slow" kernel?
>

Attached. I'm not entirely convinced about the sanity of that kernel config, so
if it might help I could repeat with a Debian packaged kernel, on the basis that
it's presumably working without error for a large number of people.

> Also, what distribution do you use (and what is its release/version)?
>

I'm using Debian unstable.


Hmm. Looking at dmesg for a 'working' kernel includes an interesting part which
I foolishly forgot to save, saying that the last 512MB of memory is
inaccessible (I was wondering where that last half-gig had gone :-)). I can go
and check exactly what it says, but I don't have the energy left for any more
reboots today. Anyway, that prompted me to try booting with mem=7168 - and that
makes the problem go away. Perhaps that will shed some light on things.

Thanks,
Nye

Download attachment "dmesg.2.6.31-09061-g6d7f18f-dirty" of type "application/octet-stream" (44382 bytes)

Download attachment "config-2.6.31-09061-g6d7f18f-dirty" of type "application/octet-stream" (61867 bytes)