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

From: Aurelien Jarno <[email-masked]>
Date: Thu, 13 Aug 2015 22:42:46 +0200

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: [email-masked]
> Cc: "David S. Miller" <[email-masked]>
> Cc: Alexei Starovoitov <[email-masked]>
> Cc: Daniel Borkmann <[email-masked]>
> Cc: Hannes Frederic Sowa <[email-masked]>
> Cc: [email-masked]
> Signed-off-by: Markos Chandras <[email-masked]>
> ---
> 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 './bpf_analysis.py'

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

https://buildd.debian.org/status/fetch.php?pkg=linux&arch=mipsel&ver=4.2%7Erc6-1%7Eexp1&stamp=1439480000

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
[email-masked]                 http://www.aurel32.net