On 4/5/16 5:06 AM, Peter Zijlstra wrote:
On Mon, Apr 04, 2016 at 09:52:47PM -0700, Alexei Starovoitov wrote:
avoid memset in perf_fetch_caller_regs, since it's the critical path of all
tracepoints.
It's called from perf_sw_event_sched, perf_event_task_sched_in and all of
perf_trace_##call
with this_cpu_ptr(&__perf_regs[..]) which are zero initialized by perpcu_alloc
Its not actually allocated; but because its a static uninitialized
variable we get .bss like behaviour and the initial value is copied to
all CPUs when the per-cpu allocator thingy bootstraps SMP IIRC.
yes, it's .bss-like in a special section. I think static percpu still
goes through some fancy boot time init similar to dynamic.
What I tried to emphasize that either static or dynamic percpu areas
are guaranteed to be zero initialized.
and
subsequent call to perf_arch_fetch_caller_regs initializes the same fields on
all archs,
so we can safely drop memset from all of the above cases and
Indeed.
move it into
perf_ftrace_function_call that calls it with stack allocated pt_regs.
Hmm, is there a reason that's still on-stack instead of using the
per-cpu thing, Steve?
Signed-off-by: Alexei Starovoitov <a...@kernel.org>
In any case,
Acked-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Thanks for the quick review.
