linux-kernel - Re: [announce] Performance Counters for Linux, v6

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Message-ID: <7c86c4470902201524i413adea4udb4637da1053ffb5@mail.gmail.com>
Date:	Sat, 21 Feb 2009 00:24:53 +0100
From:	stephane eranian <eranian@...glemail.com>
To:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Dumazet <dada1@...mosbay.com>,
	Robert Richter <robert.richter@....com>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Anvin <hpa@...or.com>, Paul Mackerras <paulus@...ba.org>,
	"David S. Miller" <davem@...emloft.net>,
	Mike Galbraith <efault@....de>
Subject: Re: [announce] Performance Counters for Linux, v6

On Sat, Feb 21, 2009 at 12:04 AM, Corey Ashford
<cjashfor@...ux.vnet.ibm.com> wrote:
>
>
> Peter Zijlstra wrote:
>>
>> On Fri, 2009-02-20 at 14:38 -0800, Corey Ashford wrote:
>>>
>>> There may be other non-event-related changes that will not be handled
>>> quite as well in this way.  In the original email I hinted at that we may
>>> want an option for mmap'd sample buffers at some point, and so I'm not clear
>>> how you'd provide an ABI to request mmap'd buffers (you would probably need
>>> to be able to request the size and get back a pointer to the mmap'd buffer).
>>>  Would this be done through a special sys_perf_counter_open call?  Or
>>> through a subsequent ioctl call on the group leader after an open (which
>>> requires the counters to be initially disabled), etc.
>>
>> What's stopping a regular mmap() call using the fd obtained from
>> sys_perf_counter_open() ?
>
> Perhaps nothing.  I don't know why it didn't occur to me that this could be
> done.  If PCL supports this, great!
>
That has always been the way, I thought this could be done with PCL.
Except that I don't know who decides the size of the mmap().
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