Corey,

On Mon, Aug 1, 2011 at 9:39 PM, Corey Ashford
<[email protected]> wrote:
> Hi Stephane,
>
> We heard from a customer that they had some perfmon2 patches that
> allowed them to measure the amount of time a thread was running on a
> CPU, *without using a system call*.
>
> I don't recall an user-only interface like that.  Did one exist?
>
The only thing I can think of would be the user-level read access to
the counters
on x86 combined with mmap page to export the software-maintained counter.
But I eventually removed that from the tree. But that was not counting cycles
without a system call. One could argue that limiting monitoring to user level
counts the cycles without a syscall, or more precisely with going into
the kernel
for any reason.

> Regards,
>
> - Corey
>
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