From: Peter Zijlstra <peterz@infradead.org>
To: Daniel Borkmann <daniel@iogearbox.net>
Cc: alexei.starovoitov@gmail.com, 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: Wed, 17 Oct 2018 17:50:50 +0200 [thread overview]
Message-ID: <20181017155050.GM3121@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20181017144156.16639-3-daniel@iogearbox.net>
On Wed, Oct 17, 2018 at 04:41:55PM +0200, Daniel Borkmann wrote:
> @@ -73,7 +73,8 @@ static inline u64 perf_mmap__read_head(struct perf_mmap *mm)
> {
> struct perf_event_mmap_page *pc = mm->base;
> u64 head = READ_ONCE(pc->data_head);
> - rmb();
> +
> + smp_rmb();
> return head;
> }
>
> @@ -84,7 +85,7 @@ static inline void perf_mmap__write_tail(struct perf_mmap *md, u64 tail)
> /*
> * ensure all reads are done before we write the tail out.
> */
> - mb();
> + smp_mb();
> pc->data_tail = tail;
Ideally that would be a WRITE_ONCE() to avoid store tearing.
Alternatively, I think we can use smp_store_release() here, all we care
about is that the prior loads stay prior.
Similarly, I suppose, we could use smp_load_acquire() for the data_head
load above.
> }
>
> --
> 2.9.5
>
next prev parent reply other threads:[~2018-10-17 23:47 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 [this message]
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
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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