Samuel Wu <[email protected]> writes: > 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 | > +-------+----+----------+----------+ > > 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.
I left some inline comments on patch 1, but the high level concern is that encoding the SRCU index into a fake pointer to get KF_ACQUIRE/ KF_RELEASE tracking is working against the verifier rather than with it. Nothing actually prevents a BPF program from walking the list without the lock, and the whole pointer encoding trick goes away if this is done as an open-coded iterator instead. Thanks, Puranjay
