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

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Message-ID: <56428B1A.5090303@linaro.org>
Date:	Tue, 10 Nov 2015 16:26:02 -0800
From:	"Shi, Yang" <yang.shi@...aro.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	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 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 will rework it.

Yang

>
>

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