Re: [Xen-devel] performance counters

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>> Keir Fraser <keir@xxxxxxxxxxxxx> 15.03.07 12:58 >>>
>On 15/3/07 11:27, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:
>
>> In order to be meaningful and usable together with other measuring methods,
>> their use in my opinion should impose as little overhead as possible. With
>> that,
>> I wonder why per-cpu counters use atomic operations.
>
>Well, they shouldn't be. Nearly all (apart from the array/histogram ones)
>are per-cpu anyway. And even if they weren't, a few lost increments wouldn't
>matter (assuming the read and write parts of the increment are each
>themselves atomic -- otherwise you could get worse write-conflict problems
>like word tearing).

Hmm, I wouldn't want to do away with the atomicity here altogether. That,
however, would imply adding knowledge about the field name of the atomic_t
to include/xen/perfc.h (and hence imply that all architectures use the same
name here). Would you consider this acceptable?

Jan

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel