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ac4ad5c09b
v2->v1: 1. Remove the simuation of STP and the related bits. 2. Use arm64_skip_faulting_instruction for single-stepping or FEAT_BTI scenario. As Andrii pointed out, the uprobe/uretprobe selftest bench run into a counterintuitive result that nop and push variants are much slower than ret variant [0]. The root cause lies in the arch_probe_analyse_insn(), which excludes 'nop' and 'stp' from the emulatable instructions list. This force the kernel returns to userspace and execute them out-of-line, then trapping back to kernel for running uprobe callback functions. This leads to a significant performance overhead compared to 'ret' variant, which is already emulated. Typicall uprobe is installed on 'nop' for USDT and on function entry which starts with the instrucion 'stp x29, x30, [sp, #imm]!' to push lr and fp into stack regardless kernel or userspace binary. In order to improve the performance of handling uprobe for common usecases. This patch supports the emulation of Arm64 equvialents instructions of 'nop' and 'push'. The benchmark results below indicates the performance gain of emulation is obvious. On Kunpeng916 (Hi1616), 4 NUMA nodes, 64 Arm64 cores@2.4GHz. xol (1 cpus) ------------ uprobe-nop: 0.916 ± 0.001M/s (0.916M/prod) uprobe-push: 0.908 ± 0.001M/s (0.908M/prod) uprobe-ret: 1.855 ± 0.000M/s (1.855M/prod) uretprobe-nop: 0.640 ± 0.000M/s (0.640M/prod) uretprobe-push: 0.633 ± 0.001M/s (0.633M/prod) uretprobe-ret: 0.978 ± 0.003M/s (0.978M/prod) emulation (1 cpus) ------------------- uprobe-nop: 1.862 ± 0.002M/s (1.862M/prod) uprobe-push: 1.743 ± 0.006M/s (1.743M/prod) uprobe-ret: 1.840 ± 0.001M/s (1.840M/prod) uretprobe-nop: 0.964 ± 0.004M/s (0.964M/prod) uretprobe-push: 0.936 ± 0.004M/s (0.936M/prod) uretprobe-ret: 0.940 ± 0.001M/s (0.940M/prod) As shown above, the performance gap between 'nop/push' and 'ret' variants has been significantly reduced. Due to the emulation of 'push' instruction needs to access userspace memory, it spent more cycles than the other. As Mark suggested [1], it is painful to emulate the correct atomicity and ordering properties of STP, especially when it interacts with MTE, POE, etc. So this patch just focus on the simuation of 'nop'. The simluation of STP and related changes will be addressed in a separate patch. [0] https://lore.kernel.org/all/CAEf4BzaO4eG6hr2hzXYpn+7Uer4chS0R99zLn02ezZ5YruVuQw@mail.gmail.com/ [1] https://lore.kernel.org/all/Zr3RN4zxF5XPgjEB@J2N7QTR9R3/ CC: Andrii Nakryiko <andrii.nakryiko@gmail.com> CC: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Liao Chang <liaochang1@huawei.com> Acked-by: Mark Rutland <mark.rutland@arm.com> Link: https://lore.kernel.org/r/20240909071114.1150053-1-liaochang1@huawei.com [catalin.marinas@arm.com: small tweaks following MarkR's comments] Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.