Date: Sat, 21 Jan 2012 13:52:47 +1100 (EST) From: Bruce Evans <brde@optusnet.com.au> To: Andreas Tobler <andreast@FreeBSD.org> Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org, src-committers@FreeBSD.org Subject: Re: svn commit: r230390 - head/sys/conf Message-ID: <20120121131914.W1596@besplex.bde.org> In-Reply-To: <201201201849.q0KInmic054086@svn.freebsd.org> References: <201201201849.q0KInmic054086@svn.freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Fri, 20 Jan 2012, Andreas Tobler wrote:
> Log:
> Disable GUPROF on archs other than i386/amd64 since the fine details are not
> implemented.
This was intentionally not done. Just don't use config -pp on arches that
don't suppport it. "profile 2" is already left out of NOTES for all
arches except amd64, i386 and powerpc. But the configuration of "profile"
in the NOTES for these arches is broken anyway. It doesn't exist. Thus
even normal profiling is not tested by NOTES on these arches.
> Modified: head/sys/conf/kern.pre.mk
> ==============================================================================
> --- head/sys/conf/kern.pre.mk Fri Jan 20 17:25:15 2012 (r230389)
> +++ head/sys/conf/kern.pre.mk Fri Jan 20 18:49:47 2012 (r230390)
> @@ -103,11 +103,14 @@ ASM_CFLAGS= -x assembler-with-cpp -DLOCO
>
> .if defined(PROFLEVEL) && ${PROFLEVEL} >= 1
> CFLAGS+= -DGPROF -falign-functions=16
> +PROF= -pg
> .if ${PROFLEVEL} >= 2
> CFLAGS+= -DGPROF4 -DGUPROF
> -PROF= -pg -mprofiler-epilogue
> +.if ${MACHINE_CPUARCH} == "i386" || ${MACHINE_CPUARCH} == "amd64"
Style bug: unsorted tests.
> +PROF+= -mprofiler-epilogue
GUPROF is completely broken in amd64 and i386 too:
- -mprofiler-epilogue is broken in gcc-4. It used to be possible to
work around this by building kernels with gcc-3, but I think there
are now some build problems with this.
- certain optimizations break GUPROF:
- -O2 breaks it even with gcc-3
- optimizations in gcc-4 break it further. Especially, -funit-at-a-time
-finline-functions-called-once. These also break ordinary profiling,
debugging, and stack traces in debuggers and panics. These and -O2
are now the defaults :-(.
- GUPROF never worked with SMP (except in my version).
OTOH, using GUPROF with SMP avoids some deadlocks on amd64 and i386.
See MCOUNT_ENTER() and MCOUNT_EXIT() on these arches. These use an
atomic_cmpset() which deadlocks any time a trap occurs in mcount()
(since the trap code is profiled). Tracing through mcount() always
causes such traps. This bug is accidentally avoided by GUPROF, since
it doesn't pretend to support SMP so it doesn't do any cmpset- type
locking. This is fixed in my version by doing more delicate locking
in mcount() for both GUPROF and !GUPROF. All arches need this.
Other arches mostly only do intr_disable()/restore() in MCOUNT_ENTER()/
EXIT(). Thus for the SMP case they have common races instead of not-so-
common deadlocks. These arches don't pretend to support SMP any more
than GUPROF does. The exceptions are mips and sparc64. mips has the
cmpsets, and sparc64 has rdpr()/wrpr() which I think are are just
lower-level forms of interrupt disabling (they mask ALL interrupts,
while intr_disable() only masks most interrupts?) Masking of traps
too would prevent deadlocks and avoid the need for cmpsets, but is not
possible. Important traps like NMIs and debugger traps are not
maskable.
> .else
> -PROF= -pg
> +.error "GUPROF not supported on ${MACHINE_CPUARCH}."
Style bug: error messages are not terminated with a "." in KNF.
> +.endif
> .endif
> .endif
> DEFINED_PROF= ${PROF}
Bruce
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20120121131914.W1596>