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Convert net_devmem_dmabuf_binding refcount from refcount_t to percpu_ref
to optimize common-case reference counting on the hot path.
The typical devmem workflow involves binding a dmabuf to a queue
(acquiring the initial reference on binding->ref), followed by
high-volume traffic where every skb fragment acquires a reference.
Eventually traffic stops and the unbind operation releases the initial
reference. Additionally, the high traffic hot path is often multi-core.
This access pattern is ideal for percpu_ref as the first and last
reference during bind/unbind normally book-ends activity in the hot
path.
__net_devmem_dmabuf_binding_free becomes the percpu_ref callback invoked
when the last reference is dropped.
kperf test:
- 4MB message sizes
- 60s of workload each run
- 5 runs
- 4 flows
Throughput:
Before: 45.31 GB/s (+/- 3.17 GB/s)
After: 48.67 GB/s (+/- 0.01 GB/s)
Picking throughput-matched kperf runs (both before and after matched at
~48 GB/s) for apples-to-apples comparison:
Summary (averaged across 4 workers):
TX worker CPU idle %:
Before: 34.44%
After: 87.13%
RX worker CPU idle %:
Before: 5.38%
After: 9.73%
kperf before:
client: == Source
client: Tx 98.100 Gbps (735764807680 bytes in 60001149 usec)
client: Tx102.798 Gbps (770996961280 bytes in 60001149 usec)
client: Tx101.534 Gbps (761517834240 bytes in 60001149 usec)
client: Tx 82.794 Gbps (620966707200 bytes in 60001149 usec)
client: net CPU 56: usr: 0.01% sys: 0.12% idle:17.06% iow: 0.00% irq: 9.89% sirq:72.91%
client: app CPU 60: usr: 0.08% sys:63.30% idle:36.24% iow: 0.00% irq: 0.30% sirq: 0.06%
client: net CPU 57: usr: 0.03% sys: 0.08% idle:75.68% iow: 0.00% irq: 2.96% sirq:21.23%
client: app CPU 61: usr: 0.06% sys:67.67% idle:31.94% iow: 0.00% irq: 0.28% sirq: 0.03%
client: net CPU 58: usr: 0.01% sys: 0.06% idle:76.87% iow: 0.00% irq: 2.84% sirq:20.19%
client: app CPU 62: usr: 0.06% sys:69.78% idle:29.79% iow: 0.00% irq: 0.30% sirq: 0.05%
client: net CPU 59: usr: 0.06% sys: 0.16% idle:74.97% iow: 0.00% irq: 3.76% sirq:21.03%
client: app CPU 63: usr: 0.06% sys:59.82% idle:39.80% iow: 0.00% irq: 0.25% sirq: 0.05%
client: == Target
client: Rx 98.092 Gbps (735764807680 bytes in 60006084 usec)
client: Rx102.785 Gbps (770962161664 bytes in 60006084 usec)
client: Rx101.523 Gbps (761499566080 bytes in 60006084 usec)
client: Rx 82.783 Gbps (620933136384 bytes in 60006084 usec)
client: net CPU 2: usr: 0.00% sys: 0.01% idle:24.51% iow: 0.00% irq: 1.67% sirq:73.79%
client: app CPU 6: usr: 1.51% sys:96.43% idle: 1.13% iow: 0.00% irq: 0.36% sirq: 0.55%
client: net CPU 1: usr: 0.00% sys: 0.01% idle:25.18% iow: 0.00% irq: 1.99% sirq:72.80%
client: app CPU 5: usr: 2.21% sys:94.54% idle: 2.54% iow: 0.00% irq: 0.38% sirq: 0.30%
client: net CPU 3: usr: 0.00% sys: 0.01% idle:26.34% iow: 0.00% irq: 2.12% sirq:71.51%
client: app CPU 7: usr: 2.22% sys:94.28% idle: 2.52% iow: 0.00% irq: 0.59% sirq: 0.37%
client: net CPU 0: usr: 0.00% sys: 0.03% idle: 0.00% iow: 0.00% irq:10.44% sirq:89.51%
client: app CPU 4: usr: 2.39% sys:81.46% idle:15.33% iow: 0.00% irq: 0.50% sirq: 0.30%
kperf after:
client: == Source
client: Tx 99.257 Gbps (744447016960 bytes in 60001303 usec)
client: Tx101.013 Gbps (757617131520 bytes in 60001303 usec)
client: Tx 88.179 Gbps (661357854720 bytes in 60001303 usec)
client: Tx101.002 Gbps (757533245440 bytes in 60001303 usec)
client: net CPU 56: usr: 0.00% sys: 0.01% idle: 6.22% iow: 0.00% irq: 8.68% sirq:85.06%
client: app CPU 60: usr: 0.08% sys:12.56% idle:87.21% iow: 0.00% irq: 0.08% sirq: 0.05%
client: net CPU 57: usr: 0.00% sys: 0.05% idle:69.53% iow: 0.00% irq: 2.02% sirq:28.38%
client: app CPU 61: usr: 0.11% sys:13.40% idle:86.36% iow: 0.00% irq: 0.08% sirq: 0.03%
client: net CPU 58: usr: 0.00% sys: 0.03% idle:70.04% iow: 0.00% irq: 3.38% sirq:26.53%
client: app CPU 62: usr: 0.10% sys:11.46% idle:88.31% iow: 0.00% irq: 0.08% sirq: 0.03%
client: net CPU 59: usr: 0.01% sys: 0.06% idle:71.18% iow: 0.00% irq: 1.97% sirq:26.75%
client: app CPU 63: usr: 0.10% sys:13.10% idle:86.64% iow: 0.00% irq: 0.10% sirq: 0.05%
client: == Target
client: Rx 99.250 Gbps (744415182848 bytes in 60003297 usec)
client: Rx101.006 Gbps (757589737472 bytes in 60003297 usec)
client: Rx 88.171 Gbps (661319475200 bytes in 60003297 usec)
client: Rx100.996 Gbps (757514792960 bytes in 60003297 usec)
client: net CPU 2: usr: 0.00% sys: 0.01% idle:28.02% iow: 0.00% irq: 1.95% sirq:70.00%
client: app CPU 6: usr: 2.03% sys:87.20% idle:10.04% iow: 0.00% irq: 0.37% sirq: 0.33%
client: net CPU 3: usr: 0.00% sys: 0.00% idle:27.63% iow: 0.00% irq: 1.90% sirq:70.45%
client: app CPU 7: usr: 1.78% sys:89.70% idle: 7.79% iow: 0.00% irq: 0.37% sirq: 0.34%
client: net CPU 0: usr: 0.00% sys: 0.01% idle: 0.00% iow: 0.00% irq: 9.96% sirq:90.01%
client: app CPU 4: usr: 2.33% sys:83.51% idle:13.24% iow: 0.00% irq: 0.64% sirq: 0.26%
client: net CPU 1: usr: 0.00% sys: 0.01% idle:27.60% iow: 0.00% irq: 1.94% sirq:70.43%
client: app CPU 5: usr: 1.88% sys:89.61% idle: 7.86% iow: 0.00% irq: 0.35% sirq: 0.27%
Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20260107-upstream-precpu-ref-v2-v2-1-a709f098b3dc@meta.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. Quick Start ----------- * Report a bug: See Documentation/admin-guide/reporting-issues.rst * Get the latest kernel: https://kernel.org * Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst * Join the community: https://lore.kernel.org/ Essential Documentation ----------------------- All users should be familiar with: * Building requirements: Documentation/process/changes.rst * Code of Conduct: Documentation/process/code-of-conduct.rst * License: See COPYING Documentation can be built with make htmldocs or viewed online at: https://www.kernel.org/doc/html/latest/ Who Are You? ============ Find your role below: * New Kernel Developer - Getting started with kernel development * Academic Researcher - Studying kernel internals and architecture * Security Expert - Hardening and vulnerability analysis * Backport/Maintenance Engineer - Maintaining stable kernels * System Administrator - Configuring and troubleshooting * Maintainer - Leading subsystems and reviewing patches * Hardware Vendor - Writing drivers for new hardware * Distribution Maintainer - Packaging kernels for distros For Specific Users ================== New Kernel Developer -------------------- Welcome! Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst Communication and Support ========================= * Mailing Lists: https://lore.kernel.org/ * IRC: #kernelnewbies on irc.oftc.net * Bugzilla: https://bugzilla.kernel.org/ * MAINTAINERS file: Lists subsystem maintainers and mailing lists * Email Clients: Documentation/process/email-clients.rst