Hi, The goal of this email is to try and figure how we want to track/limit the number of kernel threads created by vhost devices. Background: ----------- For vhost-scsi, we've hit a issue where the single vhost worker thread can't handle all IO the being sent from multiple queues. IOPs is stuck at around 500K. To fix this, we did this patchset: https://lore.kernel.org/linux-scsi/20210525180600.6349-1-michael.christie@xxxxxxxxxx/ which allows userspace to create N threads and map them to a dev's virtqueues. With this we can get around 1.4M IOPs. Problem: -------- While those patches were being reviewed, a concern about tracking all these new possible threads was raised here: https://lore.kernel.org/linux-scsi/YL45CfpHyzSEcAJv@stefanha-x1.localdomain/ To save you some time, the question is what does other kernel code using the kthread API do to track the number of kernel threads created on behalf of a userspace thread. The answer is they don't do anything so we will have to add that code. I started to do that here: https://lkml.org/lkml/2021/6/23/1233 where those patches would charge/check the vhost device owner's RLIMIT_NPROC value. But, the question of if we really want to do this has come up which is why I'm bugging lists like libvirt now. Question/Solution: ------------------ I'm bugging everyone so we can figure out: If we need to specifically track the number of kernel threads being made for the vhost kernel use case by the RLIMIT_NPROC limit? Or, is it ok to limit the number of devices with the RLIMIT_NOFILE limit. Then each device has a limit on the number of threads it can create.
