linux-kernel - Re: [patch 13/19] GTOD: Mark TSC unusable for highres timers

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: <20061110005020.4538e095.akpm@osdl.org>
Date:	Fri, 10 Nov 2006 00:50:20 -0800
From:	Andrew Morton <akpm@...l.org>
To:	tglx@...utronix.de
Cc:	Andi Kleen <ak@...e.de>, john stultz <johnstul@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Len Brown <lenb@...nel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Roman Zippel <zippel@...ux-m68k.org>
Subject: Re: [patch 13/19] GTOD: Mark TSC unusable for highres timers

On Fri, 10 Nov 2006 09:10:06 +0100
Thomas Gleixner <tglx@...utronix.de> wrote:

> On Fri, 2006-11-10 at 06:10 +0100, Andi Kleen wrote:
> > > >  		verify_tsc_freq_timer.function = verify_tsc_freq;
> > > >  		verify_tsc_freq_timer.expires =
> > > 
> > > 
> > > Hmmm. I wish this patch was unnecessary, but I don't see an easy
> > > solution. 
> > 
> > Very sad. This will make a lot of people unhappy, even to the point
> > where they might prefer disabling noidlehz over super slow gettimeofday. 
> > I assume you at least have a suitable command line option for that, right?
> 
> Yes it is sad. And the sadest part is that AMD and Intel have been asked
> to fix that more than 5 years ago. They did not get their brain straight
> and now we are the dimwits.
> 
> > Can we get a summary on which systems the TSC is considered unstable?
> > Normally we assume if it's stable enough for gettimeofday it should
> > be stable enough for longer delays too.
> 
> TSC is simply a nightmare:
> 
> - Frequency changes with CPU clock
> - Unsynced across CPUs
> - Stops in C3, which makes it completely unusable
> 
> Once you take away periodic interrupts it is simply broken. AMD and
> Intel can run in circels, it does not get better.
> 

What is the actual problem?  verify_tsc_freq()?

If so, could that function use the PIT/pmtimer/etc for working out if
the TSC is bust, rather than directly using jiffies?
-
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/