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From: Daniel Borkmann <daniel@iogearbox.net>
To: Yonghong Song <yhs@fb.com>
Cc: bpf@vger.kernel.org, Alexei Starovoitov <ast@fb.com>,
	kernel-team@fb.com, Jiong Wang <jiong.wang@netronome.com>
Subject: Re: [PATCH bpf-next v2] tools/bpf: turn on llvm alu32 attribute by default
Date: Tue, 22 Oct 2019 21:29:53 +0200	[thread overview]
Message-ID: <20191022192953.GB31343@pc-66.home> (raw)
In-Reply-To: <20191022043119.2625263-1-yhs@fb.com>

On Mon, Oct 21, 2019 at 09:31:19PM -0700, Yonghong Song wrote:
> llvm alu32 was introduced in llvm7:
>   https://reviews.llvm.org/rL325987
>   https://reviews.llvm.org/rL325989
> Experiments showed that in general performance
> is better with alu32 enabled:
>   https://lwn.net/Articles/775316/
> 
> This patch turned on alu32 with no-flavor test_progs
> which is tested most often. The flavor test at
> no_alu32/test_progs can be used to test without
> alu32 enabled. The Makefile check for whether
> llvm supports '-mattr=+alu32 -mcpu=v3' is
> removed as llvm7 should be available for recent
> distributions and also latest llvm is preferred
> to run bpf selftests.
> 
> Note that jmp32 is checked by -mcpu=probe and
> will be enabled if the host kernel supports it.
> 
> Cc: Jiong Wang <jiong.wang@netronome.com>
> Acked-by: Andrii Nakryiko <andriin@fb.com>
> Signed-off-by: Yonghong Song <yhs@fb.com>

Applied, thanks!

Would it make sense to include -mattr=+alu32 also into -mcpu=probe
on LLVM side or is the rationale to not do it that this causes a
penalty for various other, non-x86 archs when done by default
(although they could opt-out at the same time via -mattr=-alu32)?

  reply	other threads:[~2019-10-22 19:29 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-22  4:31 [PATCH bpf-next v2] tools/bpf: turn on llvm alu32 attribute by default Yonghong Song
2019-10-22 19:29 ` Daniel Borkmann [this message]
2019-10-23  2:27   ` Yonghong Song
2019-10-24 22:23     ` Jiong Wang
2019-10-25 21:42       ` Yonghong Song

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