linux-kernel - Re: [kvm-devel] [PATCH/RFC 3/4]Introduce "account modifiers" mechanism

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Message-Id: <200708171532.32850.borntraeger@de.ibm.com>
Date:	Fri, 17 Aug 2007 15:32:32 +0200
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	Laurent Vivier <Laurent.Vivier@...l.net>
Cc:	Avi Kivity <avi@...ranet.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	kvm-devel <kvm-devel@...ts.sourceforge.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	virtualization <virtualization@...ts.linux-foundation.org>
Subject: Re: [kvm-devel] [PATCH/RFC 3/4]Introduce "account modifiers"	mechanism

Am Freitag, 17. August 2007 schrieb Laurent Vivier:
> > The normal user/system accounting has the same issue, no?  Whereever we
> > happen to land (kernel or user) gets the whole tick.
> 
> Yes... but perhaps I should rewrite this too ;-)

If you look further, you will see, that this was actually rewritten in 2.6.12 
and thats why we have cputime_t. The infrastructure is currently only used by 
s390 and ppc64. On s390 we use our cpu timer to get the current time on each 
syscall/irq/context switch etc to get precise accounting data for 
system/user/irq/softirq/nice. We also get steal time (this is interesting for 
the guest: how much of my cpu was actually not available because the 
hypervisor scheduled me away). I dont know enough about other architectures  
to say which one could exploit this infrastructure as well.

The current git tree is somewhat broken for CONFIG_VIRT_CPU_ACCOUTING due to 
the accouting changes introduced by CFS - we work on this.

If you are interested in the cputime stuff, you can have a look at 
arch/s390/kernel/vtime.c (account_system_vtime, account_vtime) as well as:

http://git.kernel.org/?p=linux/kernel/git/torvalds/old-2.6-bkcvs.git;a=commit;h=6be7071fdd321c206b1ee7a3e534782f25572830
for the first introduction and
http://git.kernel.org/?p=linux/kernel/git/torvalds/old-2.6-bkcvs.git;a=commit;h=db59f519d37f80683f3611927f6b5c3bdfc0f9e6
for the s390 exploitation.

Christian
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