linux-kernel - Re: [PATCH 1/5] perf events: add support for realtime clock attribute

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Message-ID: <4D865A3E.9040605@cisco.com>
Date:	Sun, 20 Mar 2011 13:49:18 -0600
From:	David Ahern <daahern@...co.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	acme@...stprotocols.net, mingo@...e.hu, peterz@...radead.org,
	fweisbec@...il.com, paulus@...ba.org
Subject: Re: [PATCH 1/5] perf events: add support for realtime clock attribute



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
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