stephane eranian wrote:
> On Fri, Nov 20, 2009 at 12:06 AM, Corey Ashford
> <cjash...@linux.vnet.ibm.com> wrote:
>> Hi Stephane,
>>
>> I am testing an implementation of libpfm4, and ran into some curious
>> behavior with the plm field in the perf_event_attr structure. The code
>> makes it appear to be intentional, but I thought I'd run this by you to see
>> if it's what you had intended.
>>
>> If I specify an event, such as PM_RUN_CYC:i, and I don't specify any u,k, or
>> h modifiers, none of the exclude_* bits in the perf_events attribute record
>> get set. This seems ok; users may want to have events counted in all
>> privilege levels by default.
>>
>> However, if I specify "PM_RUN_CYC:i:k=0", saying I don't want kernel
>> samples, I actually get all samples, because of this code:
>>
>> if (perf_attrs.plm) {
>> hw->exclude_user = !(perf_attrs.plm & PFM_PLM3);
>> hw->exclude_kernel = !(perf_attrs.plm & PFM_PLM0);
>> hw->exclude_hv = !(perf_attrs.plm & PFM_PLMH);
>> }
>>
>> perf_attrs.plm is set to zero, if I set k=0. If I were using this
>> interface, I'd probably want hw->exclude_kernel to be set to 1.
>>
> You are right, I think there is a problem there.
>
> I think it is okay to have by default: measure everything
>
> The problem is that there is something missing in perf_attrs.
> One way to make it work could be to have
> perf_attrs.plm = PLM0|PLM3 to match the default settings and
> then have the model specific code, toggle this if the plm is not set.
> For instance,
>
> if (!reg.sel_os)
> perf_attrs.plm &= ~PLM0
>
> So you would do:
> perf.attrs = PLM0|PLM3;
> excl_u = excl_k = 0;
>
> get_encoding(, ..., &perf_attrs);
>
> if (!(perf_attrs.plm & PLM0))
> excl_k = 1
>
> if (!(perf_attrs.plm & PLM3))
> excl_u = 1
I think one of the issues here is that the user doesn't know what the default
is. So he doesn't know when he needs to clear or set the bits. If the default
is user+kernel+hypervisor, then only "u=0" (etc.) can be specified to change
that. "u" or "u=1" would have no effect since all bits are set to true by
default. Or am I missing something here?
Maybe we need an API function to obtain the defaults for each legal modifier?
Tools could then display the defaults and the user can choose to modify those
defaults, if desired.
I think this function would have somewhat wider use too: events may have
per-event defaults for modifiers. If this function was available, the encoding
function could use it internally as well when encoding an event.
I have a vague feeling that I'm making this too complex, but I don't see other
alternatives at the moment.
Any other thoughts would be appreciated.
Regards,
- Corey
Corey Ashford
Software Engineer
IBM Linux Technology Center, Linux Toolchain
Beaverton, OR
503-578-3507
cjash...@us.ibm.com
------------------------------------------------------------------------------
Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day
trial. Simplify your report design, integration and deployment - and focus on
what you do best, core application coding. Discover what's new with
Crystal Reports now. http://p.sf.net/sfu/bobj-july
_______________________________________________
perfmon2-devel mailing list
perfmon2-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/perfmon2-devel
