Re: [RFC 4/5] x86, perf: implements lwp-perf-integration (rc1)

Ingo Molnar
2011-12-19T10:56:29Z

* Robert Richter <robert.richter@amd.com> wrote:

> On 19.12.11 00:43:10, Ingo Molnar wrote:
>
> > So the question becomes, how well is it integrated: can perf
> > 'record -a + perf report', or 'perf top' use LWP, to do
> > system-wide precise [user-space] profiling and such?
>
> There is only self-monitoring of a process possible, no kernel
> and system-wide profiling. This is because we can not allocate
> memory regions in the kernel for a thread other than the
> current. This would require a complete rework of mm code.

Hm, i don't think a rework is needed: check the
vmalloc_to_page() code in kernel/events/ring_buffer.c. Right now
CONFIG_PERF_USE_VMALLOC is an ARM, MIPS, SH and Sparc specific
feature, on x86 it turns on if CONFIG_DEBUG_PERF_USE_VMALLOC=y.

That should be good enough for prototyping the kernel/user
shared buffering approach.

Thanks,

Ingo