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Date: Tue, 10 Nov 2015 16:42:09 -0800 From: Alexei Starovoitov <alexei.starovoitov@...il.com> To: "Shi, Yang" <yang.shi@...aro.org> Cc: Eric Dumazet <eric.dumazet@...il.com>, ast@...nel.org, daniel@...earbox.net, catalin.marinas@....com, will.deacon@....com, zlim.lnx@...il.com, xi.wang@...il.com, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linaro-kernel@...ts.linaro.org Subject: Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction 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! -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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