linux-kernel - Re: [PATCH] CDROM: replace jiffies busyloop with msleep

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <465497E8.6060300@gmail.com>
Date:	Wed, 23 May 2007 21:37:12 +0200
From:	Rene Herman <rene.herman@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Jeff Garzik <jeff@...zik.org>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH] CDROM: replace jiffies busyloop with msleep

On 05/23/2007 09:28 PM, Ingo Molnar wrote:

> * Rene Herman <rene.herman@...il.com> wrote:
> 
>> The trouble there is that unless you poll the bloody thing like mad 
>> too much of the Q subchannels passes below you and you need a huge 
>> number of retries to get anything out of it. I noticed when I started 
>> adding audio bits that the driver took full seconds to complete some 
>> audio requests while the old driver was snappy in that regard. When I 
>> replaced our sleeping loop with a busy-wait same as the original the 
>> snappyness returned and moreover, reading the TOC from the CD went 
>> from something close to a minute to approximately a second. Thought 
>> that minute was just because I was dealing with an old junk 1-speed 
>> drive...
> 
> ouch ...

Indeed...

> then i guess the right approach is to not use jiffies but to use a 
> calculated number of udelay(10) calls or so.

I'm not sure that will do -- the disc is still spinning below us while we're 
delaying/sleeping. Alan just now suggested checking need_resched which 
sounds like okay advice. I'll be trying what still works...

(given that noone uses these drives for anything serious anymore I'm in fact 
also not overly worried about being a busy-looping pig and just saying "this 
hardware sucks, why are you using it?").

Rene.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/