linux-kernel - Re: [PATCH] raise tsc clocksource rating

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]

Date:	Tue, 30 Oct 2007 10:02:18 -0200
From:	Glauber de Oliveira Costa <gcosta@...hat.com>
To:	Zachary Amsden <zach@...are.com>
CC:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, rusty@...tcorp.com.au, jeremy@...p.org,
	--cc@...hat.com, avi@...amnet.com, kvm-devel@...ts.sourceforge.net,
	Glauber de Oliveira Costa <glauber@....localdomain>,
	Dan Hecht <dhecht@...are.com>,
	Garrett Smith <garrett@...are.com>
Subject: Re: [PATCH] raise tsc clocksource rating

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Zachary Amsden escreveu:
> On Tue, 2007-10-30 at 00:02 +0100, Ingo Molnar wrote:
>> * Zachary Amsden <zach@...are.com> wrote:
> 
>>> Not every guest support paravirt, but for correctness, all guests 
>>> require TSC, which must be exposed all the way up to userspace, no 
>>> matter what the efficiency or accuracy may be.
>> but if there's a perfect TSC available (there is such hardware) then the 
>> TSC _is_ the best clocksource. Paravirt now turns it off unconditionally 
>> in essence.
> 
> No, if no paravirt clocksource is detected, nothing can override the
> perfect TSC hardware clocksource rating of 400.  And if a paravirt
> clocksource is detected, it is always better than TSC.

Why always? tsc is the best possible alternative the _platform_ can
provide. So the paravirt clocksource will be at best, as good as tsc.
And if it is the case: why bother with communication mechanisms of all
kinds, calculations, etc, if we can just read the tsc?

Noting again: If the tsc does not arrive accurate to the guest, it will
fail the tsc clocksource tests. So it will be rated zero anyway



-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.7 (GNU/Linux)
Comment: Using GnuPG with Remi - http://enigmail.mozdev.org

iD8DBQFHJx1KjYI8LaFUWXMRAv0hAJ4sj0Z1FraYrgbU5Mj0pWOJGk6jtwCfc5xL
jpTC273X0oqPTCR7NcVHJOI=
=WPzV
-----END PGP SIGNATURE-----
-
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/