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From: Denis Vlasenko <vda@port.imtp.ilyichevsk.odessa.ua>
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To: willy tarreau <wtarreau@yahoo.fr>, Bill Davidsen <davidsen@tmr.com>
Subject: Re: [ANNOUNCE] CMOV emulation for 2.4.19-rc1
Date: Tue, 2 Jul 2002 10:03:46 -0200
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Cc: Willy TARREAU <willy@w.ods.org>, willy@meta-x.org,
       linux-kernel@vger.kernel.org, Ronald.Wahl@informatik.tu-chemnitz.de
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On 2 July 2002 04:31, willy tarreau wrote:
> > 1.big red letters 'CMOV EMULATION' across the screen? :-)
> > 2.Scroll lock LED inverted each time CMOV is triggered?
> > 3.Printk at kernel init time:
> > "Emergency rescue kernel with CMOV emulation: can
> > be very slow, not for production use!" ?
>
> perhaps not, but we could send an alert message on
> the system console the first time an instruction is
> emulated, with the program's name. But nothing more,
> else we'll have to modify the task struct to include
> counters, and I really don't want that.
>
> > Of course (1) is a joke.
>
> so (2) isn't ? and you talk about overhead of 3 IFs

(2) is a half-joke, so to say. It woulda be funny to see
on lkml:

From: JRLuser@host.com
Subj: mailer crawls like on 286 and scroll LED blinks!!!

Everyone will immediately realize what's going on.
This will save us chasing non-existent performance 
problems. But it will cost _many_ cycles each fault.

Seriously, I think (3) is best. Why?

> an alert message on the system console
> the first time an instruction is emulated

is a printk(KERN_EMERG...), it can go unnoticed
too (all logs go to file only or user in X)
_and_ it incurs penalty on each fault.
 
> > 3.Printk at kernel init time:
> > "Emergency rescue kernel with CMOV emulation: can
> > be very slow, not for production use!" ?

is non-suppressable (unless user is stupid enough
to suppress ALL kernel boot messages) and have no penalty.
--
vda
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