linux-kernel - Re: [RFC] perf: need to expose sched_clock to correlate user samples with kernel samples

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: <515C34BF.6060508@gmail.com>
Date:	Wed, 03 Apr 2013 07:55:11 -0600
From:	David Ahern <dsahern@...il.com>
To:	Stephane Eranian <eranian@...gle.com>
CC:	John Stultz <john.stultz@...aro.org>,
	Pawel Moll <pawel.moll@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Anton Blanchard <anton@...ba.org>,
	Will Deacon <Will.Deacon@....com>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Pekka Enberg <penberg@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Robert Richter <robert.richter@....com>
Subject: Re: [RFC] perf: need to expose sched_clock to correlate user samples
 with kernel samples

On 4/3/13 3:17 AM, Stephane Eranian wrote:
> I haven't done any specific testing with either approach yet. The goal is to
> use this perf timestamp to correlate user level events to hardware
> events recorded
> by the kernel. I would assume there would be situations where those user events
> could be on the critical path, and thus the timestamp operation would have to be
> as efficient as possible. The vdso approach would be ideal.
>
>>
>> The performance/speed depends on how often is called. I have no idea what
>> Stephane's use case is but for me it is to correlate perf_clock timestamps
>> to timeofday. In my perf-based daemon that tracks process schedulings, I
>> update the correlation every 5-10 minutes.
>>
> I was more thinking along the lines of runtime environments like Java where
> a JIT compiler is invoked frequently and you need to correlate samples in the
> native code with Java source. For that, the JIT compiler has to emit mapping
> tables which have to be timestamped as address ranges may be re-used.

What's the advantage of changing apps -- like the JIT compiler -- to 
emit perf based timestamps versus having perf emit existing timestamps? 
ie., monotonic and realtime clocks already have vdso mappings for 
userspace with well known performance characteristics. Why not have perf 
convert its perf_clock timestamps into monotonic or realtime when 
dumping events?

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/