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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Daniel Borkmann <daniel@iogearbox.net>
Cc: Peter Zijlstra <peterz@infradead.org>,
	paulmck@linux.vnet.ibm.com, will.deacon@arm.com, acme@redhat.com,
	yhs@fb.com, john.fastabend@gmail.com, netdev@vger.kernel.org
Subject: Re: [PATCH bpf-next 2/3] tools, perf: use smp_{rmb,mb} barriers instead of {rmb,mb}
Date: Thu, 18 Oct 2018 08:33:09 -0700	[thread overview]
Message-ID: <20181018153307.ayvmq6du3gnsyvro@ast-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <df1da9c7-f9b4-a482-0bbc-a6455b57a476@iogearbox.net>

On Thu, Oct 18, 2018 at 05:04:34PM +0200, Daniel Borkmann wrote:
>  #endif /* _TOOLS_LINUX_ASM_IA64_BARRIER_H */
> diff --git a/tools/arch/powerpc/include/asm/barrier.h b/tools/arch/powerpc/include/asm/barrier.h
> index a634da0..905a2c6 100644
> --- a/tools/arch/powerpc/include/asm/barrier.h
> +++ b/tools/arch/powerpc/include/asm/barrier.h
> @@ -27,4 +27,20 @@
>  #define rmb()  __asm__ __volatile__ ("sync" : : : "memory")
>  #define wmb()  __asm__ __volatile__ ("sync" : : : "memory")
> 
> +#if defined(__powerpc64__)
> +#define smp_lwsync()	__asm__ __volatile__ ("lwsync" : : : "memory")
> +
> +#define smp_store_release(p, v)			\
> +do {						\
> +	smp_lwsync();				\
> +	WRITE_ONCE(*p, v);			\
> +} while (0)
> +
> +#define smp_load_acquire(p)			\
> +({						\
> +	typeof(*p) ___p1 = READ_ONCE(*p);	\
> +	smp_lwsync();				\
> +	___p1;					\

I don't like this proliferation of asm.
Why do we think that we can do better job than compiler?
can we please use gcc builtins instead?
https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html
__atomic_load_n(ptr, __ATOMIC_ACQUIRE);
__atomic_store_n(ptr, val, __ATOMIC_RELEASE);
are done specifically for this use case if I'm not mistaken.
I think it pays to learn what compiler provides.

  reply	other threads:[~2018-10-18 23:34 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-17 14:41 [PATCH bpf-next 0/3] improve and fix barriers for walking perf rb Daniel Borkmann
2018-10-17 14:41 ` [PATCH bpf-next 1/3] tools: add smp_* barrier variants to include infrastructure Daniel Borkmann
2018-10-17 14:41 ` [PATCH bpf-next 2/3] tools, perf: use smp_{rmb,mb} barriers instead of {rmb,mb} Daniel Borkmann
2018-10-17 15:50   ` Peter Zijlstra
2018-10-17 23:10     ` Daniel Borkmann
2018-10-18  8:14       ` Peter Zijlstra
2018-10-18 15:04         ` Daniel Borkmann
2018-10-18 15:33           ` Alexei Starovoitov [this message]
2018-10-18 19:00             ` Daniel Borkmann
2018-10-19  3:53               ` Alexei Starovoitov
2018-10-19 11:02                 ` Will Deacon
2018-10-19 11:56                   ` Paul E. McKenney
2018-10-19  8:04             ` Peter Zijlstra
2018-10-19  9:44           ` Peter Zijlstra
2018-10-19 10:37             ` Daniel Borkmann
2018-10-17 14:41 ` [PATCH bpf-next 3/3] bpf, libbpf: use proper barriers in perf ring buffer walk Daniel Borkmann
2018-10-17 15:51   ` Peter Zijlstra
2018-10-17 15:03 ` [PATCH bpf-next 0/3] improve and fix barriers for walking perf rb Arnaldo Carvalho de Melo

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