drivers/base/power/Makefile | 3 +- drivers/base/power/power.h | 14 +++++++++ drivers/base/power/wakeup.c | 63 +++++++++++++++++++++++++++++++++++-- kernel/power/Kconfig | 13 ++++++++ 4 files changed, 90 insertions(+), 3 deletions(-)
This patchset adds requisite kfuncs for BPF programs to safely traverse wakeup_sources, and puts a config flag around the sysfs interface. Currently, a traversal of wakeup sources require going through /sys/class/wakeup/* or /d/wakeup_sources/*. The repeated syscalls to query sysfs is inefficient, as there can be hundreds of wakeup_sources, with each wakeup source also having multiple attributes. debugfs is unstable and insecure. Adding kfuncs to lock/unlock wakeup sources allows BPF program to safely traverse the wakeup sources list. The head address of wakeup_sources can safely be resolved through BPF helper functions or variable attributes. On a quiescent Pixel 6 traversing 150 wakeup_sources, I am seeing ~34x speedup (sampled 75 times in table below). For a device under load, the speedup is greater. +-------+----+----------+----------+ | | n | AVG (ms) | STD (ms) | +-------+----+----------+----------+ | sysfs | 75 | 44.9 | 12.6 | +-------+----+----------+----------+ | BPF | 75 | 1.3 | 0.7 | +-------+----+----------+----------+ On the memory side, between kernfs, dentry, and kmalloc, each wakeup source removed from sysfs saves at least 10kB. The initial attempts for BPF traversal of wakeup_sources was with BPF iterators [1]. However, BPF already allows for traversing of a simple list with bpf_for(), and this current patchset has the added benefit of being ~2-3x more performant than BPF iterators. [1]: https://lore.kernel.org/all/20260225210820.177674-1-wusamuel@google.com/ Samuel Wu (2): PM: wakeup: Add kfuncs to lock/unlock wakeup_sources PM: Add config flag to gate sysfs wakeup_sources drivers/base/power/Makefile | 3 +- drivers/base/power/power.h | 14 +++++++++ drivers/base/power/wakeup.c | 63 +++++++++++++++++++++++++++++++++++-- kernel/power/Kconfig | 13 ++++++++ 4 files changed, 90 insertions(+), 3 deletions(-) -- 2.53.0.959.g497ff81fa9-goog
On Fri, 20 Mar 2026 at 17:01, Samuel Wu <wusamuel@google.com> wrote: > > This patchset adds requisite kfuncs for BPF programs to safely traverse > wakeup_sources, and puts a config flag around the sysfs interface. > > Currently, a traversal of wakeup sources require going through > /sys/class/wakeup/* or /d/wakeup_sources/*. The repeated syscalls to query > sysfs is inefficient, as there can be hundreds of wakeup_sources, with each > wakeup source also having multiple attributes. debugfs is unstable and > insecure. > > Adding kfuncs to lock/unlock wakeup sources allows BPF program to safely > traverse the wakeup sources list. The head address of wakeup_sources can > safely be resolved through BPF helper functions or variable attributes. > > On a quiescent Pixel 6 traversing 150 wakeup_sources, I am seeing ~34x > speedup (sampled 75 times in table below). For a device under load, the > speedup is greater. > +-------+----+----------+----------+ > | | n | AVG (ms) | STD (ms) | > +-------+----+----------+----------+ > | sysfs | 75 | 44.9 | 12.6 | > +-------+----+----------+----------+ > | BPF | 75 | 1.3 | 0.7 | > +-------+----+----------+----------+ > > On the memory side, between kernfs, dentry, and kmalloc, each wakeup source > removed from sysfs saves at least 10kB. > > The initial attempts for BPF traversal of wakeup_sources was with BPF > iterators [1]. However, BPF already allows for traversing of a simple list > with bpf_for(), and this current patchset has the added benefit of being > ~2-3x more performant than BPF iterators. See, it ended up being faster ;-). That said, I didn't understand why you dropped the test. We still need unit tests that ensure the verifier causes the bpf_ws_lock to be released before exit, and an example program (like the one you benchmarked with) to demonstrate usage. Both are mandatory. See various *_fail.c files in progs/ and RUN_TESTS() macro for running negative tests easily. I doubt we will have any wakeup_sources in the CI environment, but the example has value nonetheless. pw-bot: cr > > [1]: https://lore.kernel.org/all/20260225210820.177674-1-wusamuel@google.com/ > > Samuel Wu (2): > PM: wakeup: Add kfuncs to lock/unlock wakeup_sources > PM: Add config flag to gate sysfs wakeup_sources > > drivers/base/power/Makefile | 3 +- > drivers/base/power/power.h | 14 +++++++++ > drivers/base/power/wakeup.c | 63 +++++++++++++++++++++++++++++++++++-- > kernel/power/Kconfig | 13 ++++++++ > 4 files changed, 90 insertions(+), 3 deletions(-) > > -- > 2.53.0.959.g497ff81fa9-goog >
On Sat, Mar 21, 2026 at 10:52 AM Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote: > [ ... ] > > > > The initial attempts for BPF traversal of wakeup_sources was with BPF > > iterators [1]. However, BPF already allows for traversing of a simple list > > with bpf_for(), and this current patchset has the added benefit of being > > ~2-3x more performant than BPF iterators. > > See, it ended up being faster ;-). Yup, thanks for the suggestion! > > That said, I didn't understand why you dropped the test. We still need > unit tests that ensure the verifier causes the bpf_ws_lock to be > released before exit, and an example program (like the one you > benchmarked with) to demonstrate usage. Both are mandatory. See > various *_fail.c files in progs/ and RUN_TESTS() macro for running > negative tests easily. I doubt we will have any wakeup_sources in the > CI environment, but the example has value nonetheless. > > pw-bot: cr > Sounds good, in v2 I can add a test for the lock/unlock kfunc. And thanks for the thorough feedback, let me take a look at the *_fail.c files and test macros.
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