Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction

From	Alexei Starovoitov <alexei.starovoitov@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction
Date	2015-11-11 01:50 +0100
Message-ID	<qtrLP-3YD-9@gated-at.bofh.it> (permalink)
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On Tue, Nov 10, 2015 at 04:26:02PM -0800, Shi, Yang wrote:
> On 11/10/2015 4:08 PM, Eric Dumazet wrote:
> >On Tue, 2015-11-10 at 14:41 -0800, Yang Shi wrote:
> >>aarch64 doesn't have native support for XADD instruction, implement it by
> >>the below instruction sequence:
> >>
> >>Load (dst + off) to a register
> >>Add src to it
> >>Store it back to (dst + off)
> >
> >Not really what is needed ?
> >
> >See this BPF_XADD as an atomic_add() equivalent.
> 
> I see. Thanks. The documentation doesn't say too much about "exclusive" add.
> If so it should need load-acquire/store-release.

I think doc is clear enough, but it can always be improved. Pls suggest a patch.
It's quite hard to write a test for atomicity in test_bpf framework, so
code review is the key. Eric, thanks for catching it!

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Thread

[PATCH 2/2] arm64: bpf: add BPF XADD instruction Yang Shi <yang.shi@linaro.org> - 2015-11-11 00:10 +0100
  Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Eric Dumazet <eric.dumazet@gmail.com> - 2015-11-11 01:10 +0100
    Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction "Shi, Yang" <yang.shi@linaro.org> - 2015-11-11 01:30 +0100
      Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Alexei Starovoitov <alexei.starovoitov@gmail.com> - 2015-11-11 01:50 +0100
        Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Z Lim <zlim.lnx@gmail.com> - 2015-11-11 04:00 +0100
          Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Arnd Bergmann <arnd@arndb.de> - 2015-11-11 10:00 +0100
            Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Will Deacon <will.deacon@arm.com> - 2015-11-11 11:30 +0100
              Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Daniel Borkmann <daniel@iogearbox.net> - 2015-11-11 11:50 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Will Deacon <will.deacon@arm.com> - 2015-11-11 13:00 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Daniel Borkmann <daniel@iogearbox.net> - 2015-11-11 13:30 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Will Deacon <will.deacon@arm.com> - 2015-11-11 13:40 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Peter Zijlstra <peterz@infradead.org> - 2015-11-11 14:00 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Daniel Borkmann <daniel@iogearbox.net> - 2015-11-11 17:00 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Will Deacon <will.deacon@arm.com> - 2015-11-11 17:30 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Alexei Starovoitov <alexei.starovoitov@gmail.com> - 2015-11-11 18:30 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction David Miller <davem@davemloft.net> - 2015-11-11 18:40 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Will Deacon <will.deacon@arm.com> - 2015-11-11 18:50 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction David Miller <davem@davemloft.net> - 2015-11-11 20:10 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Peter Zijlstra <peterz@infradead.org> - 2015-11-11 19:00 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Alexei Starovoitov <alexei.starovoitov@gmail.com> - 2015-11-11 19:20 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Peter Zijlstra <peterz@infradead.org> - 2015-11-11 19:40 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Peter Zijlstra <peterz@infradead.org> - 2015-11-11 19:50 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Peter Zijlstra <peterz@infradead.org> - 2015-11-11 19:50 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Peter Zijlstra <peterz@infradead.org> - 2015-11-11 20:00 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Alexei Starovoitov <alexei.starovoitov@gmail.com> - 2015-11-11 21:00 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Peter Zijlstra <peterz@infradead.org> - 2015-11-11 23:30 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Alexei Starovoitov <alexei.starovoitov@gmail.com> - 2015-11-12 00:50 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Peter Zijlstra <peterz@infradead.org> - 2015-11-12 10:00 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Daniel Borkmann <daniel@iogearbox.net> - 2015-11-11 20:00 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction David Miller <davem@davemloft.net> - 2015-11-11 20:10 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Peter Zijlstra <peterz@infradead.org> - 2015-11-11 20:30 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Daniel Borkmann <daniel@iogearbox.net> - 2015-11-11 20:50 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Will Deacon <will.deacon@arm.com> - 2015-11-11 19:50 +0100
                Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction David Miller <davem@davemloft.net> - 2015-11-11 20:10 +0100

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