netdev - Re: [PATCH bpf-next 2/2] libbpf, xsk: add libbpf_smp_store_release libbpf_smp_load

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Message-ID: <e052a22a-4b7b-fe38-06ad-2ad04c83dda7@intel.com>
Date:   Tue, 2 Mar 2021 09:05:15 +0100
From:   Björn Töpel <bjorn.topel@...el.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>,
        Björn Töpel <bjorn.topel@...il.com>,
        ast@...nel.org, daniel@...earbox.net, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Cc:     magnus.karlsson@...el.com, jonathan.lemon@...il.com,
        maximmi@...dia.com, andrii@...nel.org, will@...nel.org
Subject: Re: [PATCH bpf-next 2/2] libbpf, xsk: add libbpf_smp_store_release
 libbpf_smp_load_acquire

On 2021-03-01 17:10, Toke Høiland-Jørgensen wrote:
> Björn Töpel <bjorn.topel@...il.com> writes:
> 
>> From: Björn Töpel <bjorn.topel@...el.com>
>>
>> Now that the AF_XDP rings have load-acquire/store-release semantics,
>> move libbpf to that as well.
>>
>> The library-internal libbpf_smp_{load_acquire,store_release} are only
>> valid for 32-bit words on ARM64.
>>
>> Also, remove the barriers that are no longer in use.
> 
> So what happens if an updated libbpf is paired with an older kernel (or
> vice versa)?
>

"This is fine." ;-) This was briefly discussed in [1], outlined by the
previous commit!

...even on POWER.


Björn

[1] https://lore.kernel.org/bpf/20200316184423.GA14143@willie-the-truck/


> -Toke
>