linux-kernel - Re: [RFC][PATCH v2 1/7] taskstats: Add new taskstats command TASKSTATS_CMD_ATTR

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: <1289910972.2109.598.camel@laptop>
Date:	Tue, 16 Nov 2010 13:36:12 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	holzheu@...ux.vnet.ibm.com
Cc:	Shailabh Nagar <nagar1234@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Venkatesh Pallipadi <venki@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Ingo Molnar <mingo@...e.hu>, Oleg Nesterov <oleg@...hat.com>,
	John stultz <johnstul@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [RFC][PATCH v2 1/7] taskstats: Add new taskstats command
 TASKSTATS_CMD_ATTR_PIDS

On Tue, 2010-11-16 at 13:16 +0100, Michael Holzheu wrote:

> Ok, thanks. So sched_clock() seems to be a bad idea for our purposes.
> 
> An alternative approach could be to have a global counter for the task
> snapshots, which is increased each time a snapshot is created for
> userspace. In addition to that we had to add a snapshot counter field to
> the task_struct that is set to the current value of the global counter
> each time a task leaves a CPU. Then userspace could ask for all tasks
> that have been active after snapshot number x. In the response userspace
> gets all tasks that have a snapshot number bigger than x together with
> the new snapshot number y that can be used for the next query.
> 
> Still it would be useful to add a timestamp of the creation of the
> taskstats data in the response to userspace for calculating the interval
> time between two snapshots. Would the usage of ktime_get() be valid for
> that purpose?

ktime_get() can be insanely slow, but yes that's an option. Another
option is using local_clock() and living with the fact that it may be
out of sync (up to a jiffy or so) between CPUs.

The advantage of using ktime_get() as opposed to any other clock is that
userspace has access to it as well through:
clock_gettime(CLOCK_MONOTONIC), although that's arguably not too
relevant when all you're interested in is deltas.



--
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/