Re: [PATCH 6/6] MIPS: net: BPF: Introduce BPF ASM helpers

From: Aurelien Jarno
Date: Thu Aug 13 2015 - 17:05:09 EST

On 2015-06-04 11:56, Markos Chandras wrote:
> This commit introduces BPF ASM helpers for MIPS and MIPS64 kernels.
> The purpose of this patch is to twofold:
> 1) We are now able to handle negative offsets instead of either
> falling back to the interpreter or to simply not do anything and
> bail out.
> 2) Optimize reads from the packet header instead of calling the C
> helpers
> Because of this patch, we are now able to get rid of quite a bit of
> code in the JIT generation process by using MIPS optimized assembly
> code. The new assembly code makes the test_bpf testsuite happy with
> all 60 test passing successfully compared to the previous
> implementation where 2 tests were failing.
> Doing some basic analysis in the results between the old
> implementation and the new one we can obtain the following
> summary running current mainline on an ER8 board (+/- 30us delta is
> ignored to prevent noise from kernel scheduling or IRQ latencies):
> Summary: 22 tests are faster, 7 are slower and 47 saw no improvement
> with the most notable improvement being the tcpdump tests. The 7 tests
> that seem to be a bit slower is because they all follow the slow path
> (bpf_internal_load_pointer_neg_helper) which is meant to be slow so
> that's not a problem.
> Cc: netdev@xxxxxxxxxxxxxxx
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Alexei Starovoitov <ast@xxxxxxxxxxxx>
> Cc: Daniel Borkmann <dborkman@xxxxxxxxxx>
> Cc: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Signed-off-by: Markos Chandras <markos.chandras@xxxxxxxxxx>
> ---
> I have uploaded the script and the bpf result files in my LMO webspace
> in case you want to have a look. I didn't paste them in here because they
> are nearly 200 lines. Simply download all 3 files and run './'

This patch relies on R2 instructions, and thus the Linux kernel fails to
build when targetting non-R2 CPUs. See for example:

Aurelien Jarno GPG: 4096R/1DDD8C9B
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