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Date: Sun, 18 Oct 2015 11:15:16 +0000 From: Alexey Brodkin <Alexey.Brodkin@...opsys.com> To: Vineet Gupta <Vineet.Gupta1@...opsys.com> CC: Aabid Rushdi <Aabid.Rushdi@...opsys.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "peterz@...radead.org" <peterz@...radead.org>, "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>, "dvhart@...ux.intel.com" <dvhart@...ux.intel.com>, "dsahern@...il.com" <dsahern@...il.com>, "acme@...hat.com" <acme@...hat.com> Subject: Re: [RFC] perf: fix building for ARCv1 Hi Vineet, Looks like this time atomics are a must. And that really sucks! See these commits that introduce usage of atomic_xxx() all around the perf and tools it uses: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=f812d3045c2385ac16237e68b156859c4005526e http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=d3a7c489c7fd2463e3b2c3a2179c7be879dd9cb4 http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=7143849a5d6a5c623d81790d92f0033507c5b14f http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=59a51c1dc9fbb3fb4af928b852d7b35df83edd74 http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=e1ed3a5b87ed6759e16ec93f16aae83d2cc77ca2 and that's the one that introduced usage of the following generic gcc's atomics (__sync_add_and_fetch/__sync_sub_and_fetch): http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=da6d8567512df11e0473b710c07de87efde5709c So the best we may do is to implement detection of atomics in the toolchain and if there's no atomics hard stop with perf building. -Alexey On Sat, 2015-10-17 at 14:19 +0000, Vineet Gupta wrote: > On Saturday 17 October 2015 07:06 PM, Alexey Brodkin wrote: > > Perf uses atomic options and so it is required to have atomics enabled > > in toolchain. > > > > In case of ARC atomics are enabled by default for ARCv2 but disabled for > > ARCv1. Now we explicitly enable atomics for either ARC achitecture > > version so perf could be successfully built. > > > > Currently on attempt to build perf for ARCv1 you'll see tons of: > > ----------------->8----------------- > > undefined reference to `__sync_add_and_fetch_4' > > ----------------->8----------------- > > > > Still note if ARCv1 CPU is configured without LL/SC perf will crash on > > execution once "llock" instruction is attempted to be executed. > > Ok this fixes ARCompact - assuming it will have LL/SC. We do have old SoCs w/o > that support. > So what we are saying is that any arch (or a configuration thereof) which doesn't > support atomic r-m-w can't even build perf now - that sucks ! > > A better way would be to do feature test for __sync_xyz and make atomic_xxx > wrappers call __sync_xyz) vs. an empty stub. > So atleast such arches can build and do "some" perf work ! > > -Vineet > > > Cc: Vineet Gupta <vgupta@...opsys.com> > > Cc: Peter Zijlstra <peterz@...radead.org> > > Cc: Arnaldo Carvalho de Melo <acme@...nel.org> > > Signed-off-by: Alexey Brodkin <abrodkin@...opsys.com> > > --- > > tools/perf/config/Makefile | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/tools/perf/config/Makefile b/tools/perf/config/Makefile > > index 38a0853..dc7c0a8 100644 > > --- a/tools/perf/config/Makefile > > +++ b/tools/perf/config/Makefile > > @@ -47,6 +47,11 @@ ifeq ($(ARCH),arm64) > > LIBUNWIND_LIBS = -lunwind -lunwind-aarch64 > > endif > > > > +# Additional ARCH settings for ARC > > +ifeq ($(ARCH),arc) > > + CFLAGS += -matomic > > +endif > > + > > ifeq ($(NO_PERF_REGS),0) > > $(call detected,CONFIG_PERF_REGS) > > endif > >
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