runtime: support for always-on background profiling

runtime: support for always-on background profiling

[dvyukov, 2014-06-20 05:22:58]

runtime/prof.h is empty, remove?

https://codereview.appspot.com/101380044/diff/20001/src/pkg/runtime/runtime.h
File src/pkg/runtime/runtime.h (right):

https://codereview.appspot.com/101380044/diff/20001/src/pkg/runtime/runtime.h...
src/pkg/runtime/runtime.h:96: typedef	struct	ProfBuf	ProfBuf;
tab before ProfBuf;

[dvyukov, 2014-06-20 05:50:55]

https://codereview.appspot.com/101380044/diff/20001/src/pkg/runtime/proc.c
File src/pkg/runtime/proc.c (right):

https://codereview.appspot.com/101380044/diff/20001/src/pkg/runtime/proc.c#ne...
src/pkg/runtime/proc.c:2362: runtime·resetcpuprofiler(0);
I think here is some potential for deadlocking.
Currently we assume that calls to runtime·setcpuprofilerate do not race with
each other.
But if a program calls runtime·enablebgcpu during startup and concurrently user
(or some global monitoring system) calls runtime·setcpuprofilerate, then CPU
profiling can be enabled again. And then signal delivered to runtime·enablebgcpu
will deadlock on prof lock.

[dvyukov, 2014-06-21 18:30:38]

https://codereview.appspot.com/101380044/diff/20001/src/pkg/runtime/prof.c
File src/pkg/runtime/prof.c (right):

https://codereview.appspot.com/101380044/diff/20001/src/pkg/runtime/prof.c#ne...
src/pkg/runtime/prof.c:1: #include "runtime.h"
copyright?

https://codereview.appspot.com/101380044/diff/20001/src/pkg/runtime/prof.c#ne...
src/pkg/runtime/prof.c:6: runtime·newprofbuf(int32 hdrsize, int32 bufwords)
what is this hdr/hdrsize?
can we drop it?

https://codereview.appspot.com/101380044/diff/20001/src/pkg/runtime/prof.c#ne...
src/pkg/runtime/prof.c:13: size = bufwords*8 + sizeof(ProfBuf);
size = ROUND(bufwords*8 + sizeof(ProfBuf), PhysPageSize)

https://codereview.appspot.com/101380044/diff/20001/src/pkg/runtime/prof.c#ne...
src/pkg/runtime/prof.c:49: if(b->w + n - b->r > b->max) {
as of now this is x86 only at best
you need to read b->r once with atomicload and update b->w with atomicstore
and the opposite in profread

https://codereview.appspot.com/101380044/diff/20001/src/pkg/runtime/prof.c#ne...
src/pkg/runtime/prof.c:51: if(!b->full) {
this will be way simpler if you construct the overflow entry in profread:
add single overflow counter to bgprof, atomically increment it on overflow
if the counter is not zero, profread reads and sets it to zero with atomic xchg
and constructs the overflow entry
that's it

https://codereview.appspot.com/101380044/diff/20001/src/pkg/runtime/prof.c#ne...
src/pkg/runtime/prof.c:98: *wp = g->proftag; // prof tag
profiler does not run in the context of a user goroutine, you need to pass gp
from above

https://codereview.appspot.com/101380044/diff/20001/src/pkg/runtime/prof.c#ne...
src/pkg/runtime/prof.c:166: runtime·EnableProfCPU(intgo hz, intgo bufwords)
for 1.4 it will need to be in Go
probably all user-callable functions here just need to switch to g0

https://codereview.appspot.com/101380044/diff/20001/src/pkg/runtime/prof.c#ne...
src/pkg/runtime/prof.c:287: runtime·printf("read %d\n", ret);
remove

https://codereview.appspot.com/101380044/diff/20001/src/pkg/runtime/prof.go
File src/pkg/runtime/prof.go (right):

https://codereview.appspot.com/101380044/diff/20001/src/pkg/runtime/prof.go#n...
src/pkg/runtime/prof.go:1: package runtime
copyright?

https://codereview.appspot.com/101380044/diff/20001/src/pkg/runtime/prof_test.go
File src/pkg/runtime/prof_test.go (right):

https://codereview.appspot.com/101380044/diff/20001/src/pkg/runtime/prof_test...
src/pkg/runtime/prof_test.go:1: package runtime_test
copyright?