linux-kernel - Re: [PATCH v2 1/2] perf: Add sampling of the raw monotonic clock

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: <5425BD94.4030006@gmail.com>
Date:	Fri, 26 Sep 2014 13:25:08 -0600
From:	David Ahern <dsahern@...il.com>
To:	Pawel Moll <pawel.moll@....com>, Namhyung Kim <namhyung@...nel.org>
CC:	Richard Cochran <richardcochran@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	John Stultz <john.stultz@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] perf: Add sampling of the raw monotonic clock

On 9/26/14, 9:05 AM, Pawel Moll wrote:
> To do the correlation you need both timestamps to be "taken"
> simultaneously:
>
>          perf event     user event
>         -----O--------------+-------------O------> t_mono
>              :              |             :
>              :              V             :
>         -----O----------------------------O------> t_perf
>
> Of course it's not possible get both values literally at the same time,
> but placing them in a atomic context a couple of instructions from each
> other still gives pretty good results. The larger this distance is, the

An early patchset on this topic added the realtime clock as an event and 
an ioctl was used to push a sample into the event stream. In that case 
you have wall clock and perf-clock samples taken in the same kernel 
context and about as close together as you can get.

https://lkml.org/lkml/2011/2/27/158
https://lkml.org/lkml/2011/2/27/159

David
--
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/