s390/bpf: Inline smp_processor_id and current_task

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Inline these calls in bpf jit:
 - bpf_get_smp_processor_id()
 - bpf_get_current_task()
 - bpf_get_current_task_btf()

s390 has a 8 KiB per-CPU prefix area in the CPU's
virtual address space, called the lowcore. It is a
struct that contains the cpu number and a pointer
to the current task. These are exactly the values
returned by the BPF helpers.

Emit a load from the lowcore instead of a helper
function call.

JIT output for `bpf_get_smp_processor_id`:

 Before:                       After:
---------------               ----------------
brasl   %r14,0x3ffe0385460    ly      %r14,928
lgr     %r14,%r2

JIT output for `bpf_get_current_task`:

 Before:                        After:
---------------                ----------------
brasl   %r14,0x3ffe0362a90     lg      %r14,832
lgr     %r14,%r2

Benchmark using [1] on KVM(virtme-ng).

./benchs/run_bench_trigger.sh glob-arr-inc arr-inc hash-inc

+---------------+--------------------+--------------------+--------------+
|     Name      |       Before       |       After        |   % change   |
|---------------+--------------------+--------------------+--------------|
| glob-arr-inc  | 244.954 ± 0.654M/s | 278.501 ± 0.834M/s |   + 13.70%   |
| arr-inc       | 311.597 ± 1.016M/s | 313.610 ± 0.331M/s |   + 0.65%    |
| hash-inc      | 47.421 ± 0.017M/s  | 47.600 ± 0.004M/s  |   + 0.38%    |
+---------------+--------------------+--------------------+--------------+

[1] 8dec900975

Signed-off-by: Maxim Khmelevskii <max@linux.ibm.com>
Reviewed-by: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/r/20260414142930.528751-1-max@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

...

This commit is contained in:

Maxim Khmelevskii 2026-04-14 16:29:26 +02:00 • committed by Alexei Starovoitov

parent c8f0ee969f

commit 9012cf2491

1 changed files with 37 additions and 0 deletions

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arch/s390/net/bpf_jit_comp.c

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