Re: dm-crypt performance regression due to workqueue changes

Hello, On Sat, Jun 29, 2024 at 08:15:56PM +0200, Mikulas Patocka wrote: > With 6.5, we get 3600MiB/s; with 6.6 we get 1400MiB/s. > > The reason is that virt-manager by default sets up a topology where we > have 16 sockets, 1 core per socket, 1 thread per core. And that workqueue > patch avoids moving work items across sockets, so it processes all > encryption work only on one virtual CPU. > > The performance degradation may be fixed with "echo 'system' > >/sys/module/workqueue/parameters/default_affinity_scope" - but it is > regression anyway, as many users don't know about this option. > > How should we fix it? There are several options: > 1. revert back to 'numa' affinity > 2. revert to 'numa' affinity only if we are in a virtual machine > 3. hack dm-crypt to set the 'numa' affinity for the affected workqueues > 4. any other solution? Do you happen to know why libvirt is doing that? There are many other implications to configuring the system that way and I don't think we want to design kernel behaviors to suit topology information fed to VMs which can be arbitrary. Thanks.