Messages in this thread | | | Subject | Re: [PATCH 5/5] MIPS: Add support for eBPF JIT. | From | David Daney <> | Date | Fri, 26 May 2017 12:20:32 -0700 |
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On 05/26/2017 12:09 PM, Daniel Borkmann wrote: > On 05/26/2017 05:39 PM, David Daney wrote: >> On 05/26/2017 08:14 AM, Daniel Borkmann wrote: >>> On 05/26/2017 02:38 AM, David Daney wrote: >>>> Since the eBPF machine has 64-bit registers, we only support this in >>>> 64-bit kernels. As of the writing of this commit log test-bpf is >>>> showing: >>>> >>>> test_bpf: Summary: 316 PASSED, 0 FAILED, [308/308 JIT'ed] >>>> >>>> All current test cases are successfully compiled. >>>> >>>> Signed-off-by: David Daney <david.daney@cavium.com> >>> >>> Awesome work! >>> >>> Did you also manage to run tools/testing/selftests/bpf/ fine with >>> the JIT enabled? >> >> I haven't done that yet, I will before the next revision. >> >>> [...] >>>> +struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog) >>>> +{ >>>> + struct jit_ctx ctx; >>>> + unsigned int alloc_size; >>>> + >>>> + /* Only 64-bit kernel supports eBPF */ >>>> + if (!IS_ENABLED(CONFIG_64BIT) || !bpf_jit_enable) >>> >>> Isn't this already reflected by the following? >>> >>> select HAVE_EBPF_JIT if (64BIT && !CPU_MICROMIPS) >> >> Not exactly. The eBPF JIT is in the same file as the classic-BPF JIT, >> so when HAVE_EBPF_JIT is false this will indeed never be called. But >> the kernel would otherwise contain all the JIT code. >> >> By putting in !IS_ENABLED(CONFIG_64BIT) we allow gcc to eliminate all >> the dead code when compiling the JITs. > > Side-effect would still be that for cBPF you go through the cBPF > JIT instead of letting the kernel convert all cBPF to eBPF and > later on go through your eBPF JIT. If you still prefer to have > everything in one single file and let gcc eliminate dead code > then you can just do single line change ... > > void bpf_jit_compile(struct bpf_prog *fp) > { > struct jit_ctx ctx; > unsigned int alloc_size, tmp_idx; > > if (IS_ENABLED(CONFIG_HAVE_EBPF_JIT) || !bpf_jit_enable) > return;
Yes. In fact I did that for testing.
The cBPF JIT generates smaller code for:
test_bpf: #274 BPF_MAXINSNS: ld_abs+get_processor_id jited:1 44128 PASS
When we attempt to use the eBPF JIT for this, some of the MIPS branch instructions cannot reach their targets (+- 32K instructions). I didn't feel like fixing the code generation quite yet to handle branches that span more than 32K instructions, so I left the cBPF in place so I could claim that all of the test cases were JITed :-)
For the next revision of the patch I will revisit this.
David.
> [...] > } > > ... and bpf_prog_ebpf_jited() et al wouldn't need to be changed > in the core, which are used in kallsyms, and kernel will then > also be able to automatically JIT all of seccomp-BPF and the > missing cBPF extensions we have through the eBPF JIT w/o extra > work.
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