From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Ahern <daahern@cisco.com>
Subject: Re: [PATCH 1/5] perf events: add support for realtime clock attribute
Date: Sun, 20 Mar 2011 13:49:18 -0600
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To: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, acme@ghostprotocols.net, mingo@elte.hu, peterz@infradead.org, fweisbec@gmail.com, paulus@samba.org



On 03/20/11 13:08, Thomas Gleixner wrote:
> On Sun, 20 Mar 2011, David Ahern wrote:
>> +
>> +	if (sample_type & PERF_SAMPLE_REALTIME)
>> +		data->realtime = ktime_to_ns(ktime_get_real());
> 
> That's going to live lock on any sample which happens to hit in a
> xtime_lock write locked section. I knew why I suggested adding
> tracepoints to the timekeeping code :)

Hmmm.... Can you give an example of when perf samples could be generated
with xtime write locked? What are the rules for when ktime_get_real can
be invoked?

David

> 
> Thanks,
> 
> 	tglx