linux-kernel - RE: [patch] x86, perf_counter, bts: add bts to perf

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Message-ID: <928CFBE8E7CB0040959E56B4EA41A77EC1BFF07F@irsmsx504.ger.corp.intel.com>
Date:	Fri, 7 Aug 2009 12:51:04 +0100
From:	"Metzger, Markus T" <markus.t.metzger@...el.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"hpa@...or.com" <hpa@...or.com>,
	"markus.t.metzger@...il.com" <markus.t.metzger@...il.com>,
	"oleg@...hat.com" <oleg@...hat.com>
Subject: RE: [patch] x86, perf_counter, bts: add bts to perf_counter

>-----Original Message-----
>From: Peter Zijlstra [mailto:a.p.zijlstra@...llo.nl]
>Sent: Friday, August 07, 2009 1:45 PM
>To: Metzger, Markus T
>Cc: linux-kernel@...r.kernel.org; mingo@...e.hu; tglx@...utronix.de; hpa@...or.com;
>markus.t.metzger@...il.com; oleg@...hat.com
>Subject: Re: [patch] x86, perf_counter, bts: add bts to perf_counter
>
>On Fri, 2009-08-07 at 09:22 +0200, Markus Metzger wrote:
>> @@ -721,9 +903,13 @@ static int __hw_perf_counter_init(struct
>>         err = 0;
>>         if (!atomic_inc_not_zero(&active_counters)) {
>>                 mutex_lock(&pmc_reserve_mutex);
>> -               if (atomic_read(&active_counters) == 0 && !reserve_pmc_hardware())
>> -                       err = -EBUSY;
>> -               else
>> +               if (atomic_read(&active_counters) == 0) {
>> +                       if (!reserve_pmc_hardware())
>> +                               err = -EBUSY;
>> +                       else
>> +                               reserve_bts_hardware();
>> +               }
>> +               if (!err)
>>                         atomic_inc(&active_counters);
>>                 mutex_unlock(&pmc_reserve_mutex);
>>         }
>
>You loose the reserve_bts_hardware() error case there.


That had been intentional since I consider BTS somewhat optional. In case it is not available or
fails to initialize, e.g. out of memory, we fall back to normal profiling.

Now that I think about it again, I guess that's not what a (debugger) user would expect.
An error might be more appropriate in that case.

I'll change it.

thanks and regards,
markus.

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