Re: [announce] Performance Counters for Linux, v6

[stephane eranian <eranian@googlemail.com>]

On Sat, Feb 21, 2009 at 12:04 AM, Corey Ashford
<cjashfor@linux.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().