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Date: Tue, 10 Nov 2015 18:52:45 -0800 From: Z Lim <zlim.lnx@...il.com> To: Alexei Starovoitov <alexei.starovoitov@...il.com>, "Shi, Yang" <yang.shi@...aro.org> Cc: Eric Dumazet <eric.dumazet@...il.com>, Alexei Starovoitov <ast@...nel.org>, daniel@...earbox.net, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Xi Wang <xi.wang@...il.com>, LKML <linux-kernel@...r.kernel.org>, Network Development <netdev@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, linaro-kernel@...ts.linaro.org Subject: Re: [PATCH 2/2] arm64: bpf: add BPF XADD instruction Yang, On Tue, Nov 10, 2015 at 4:42 PM, Alexei Starovoitov <alexei.starovoitov@...il.com> wrote: > 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: aarch64 supports atomic add in ARMv8.1. For ARMv8(.0), please consider using LDXR/STXR 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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