netdev - Re: [PATCH v2 0/5] Atomics support for eBPF on powerpc

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Date:   Fri, 24 Jun 2022 16:07:58 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>
To:     bpf@...r.kernel.org, Hari Bathini <hbathini@...ux.ibm.com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Cc:     Andrii Nakryiko <andrii@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jordan Niethe <jniethe5@...il.com>,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        KP Singh <kpsingh@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>, netdev@...r.kernel.org,
        Paul Mackerras <paulus@...ba.org>,
        Russell Currey <ruscur@...sell.cc>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>
Subject: Re: [PATCH v2 0/5] Atomics support for eBPF on powerpc

Hi Hari,

Hari Bathini wrote:
> This patchset adds atomic operations to the eBPF instruction set on
> powerpc. The instructions that are added here can be summarised with
> this list of kernel operations for ppc64:
> 
> * atomic[64]_[fetch_]add
> * atomic[64]_[fetch_]and
> * atomic[64]_[fetch_]or
> * atomic[64]_[fetch_]xor
> * atomic[64]_xchg
> * atomic[64]_cmpxchg
> 
> and this list of kernel operations for ppc32:
> 
> * atomic_[fetch_]add
> * atomic_[fetch_]and
> * atomic_[fetch_]or
> * atomic_[fetch_]xor
> * atomic_xchg
> * atomic_cmpxchg

Thanks for your work on this. For this series:
Reviewed-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>

> 
> The following are left out of scope for this effort:
> 
> * 64 bit operations on ppc32.
> * Explicit memory barriers, 16 and 8 bit operations on both ppc32
>   & ppc64.

The latter is a limitation of the eBPF instruction set itself today, 
rather than a powerpc-specific limitation.

> 
> The first patch adds support for bitwsie atomic operations on ppc64.
> The next patch adds fetch variant support for these instructions. The
> third patch adds support for xchg and cmpxchg atomic operations on
> ppc64. Patch #4 adds support for 32-bit atomic bitwise operations on
> ppc32. patch #5 adds support for xchg and cmpxchg atomic operations
> on ppc32.
> 
> Validated these changes successfully with atomics test cases in
> test_bpf testsuite and  test_verifier & test_progs selftests.
> With test_bpf testsuite:
> 
>   all 147 atomics related test cases (both 32-bit & 64-bit) JIT'ed
>   successfully on ppc64:
> 
>     test_bpf: Summary: 1026 PASSED, 0 FAILED, [1014/1014 JIT'ed]
> 
>   all 76 atomics related test cases (32-bit) JIT'ed successfully
>   on ppc32:
> 
>     test_bpf: Summary: 1027 PASSED, 0 FAILED, [915/1015 JIT'ed]

Indeed. In my tests, before this series, with CONFIG_BPF_JIT_ALWAYS_ON=y:
test_bpf: Summary: 894 PASSED, 132 FAILED, [882/882 JIT'ed]
test_progs --name=atomic: Summary: 0/0 PASSED, 0 SKIPPED, 2 FAILED
test_verifier 0 100: Summary: 46 PASSED, 151 SKIPPED, 0 FAILED

With your patches:
test_bpf: Summary: 1026 PASSED, 0 FAILED, [1014/1014 JIT'ed]
test_progs --name=atomic: Summary: 2/7 PASSED, 0 SKIPPED, 0 FAILED
test_verifier 0 100: Summary: 101 PASSED, 96 SKIPPED, 0 FAILED

It is nice to see all the test_bpf tests pass again on ppc64le!

Tested-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com> (ppc64le)


- Naveen