On Wed, Sep 15, 2021 at 05:19:03PM -0700, Hao Luo wrote: > Hi Roman, > > On Wed, Sep 15, 2021 at 3:04 PM Roman Gushchin <guro@xxxxxx> wrote: > > Hi Hao! > > Thanks for initiating the effort of bringing BPF to sched. I've been > looking at the potential applications of BPF in sched for some time > and I'm very excited about this work! > > My current focus has been using BPF for profiling performance and > exporting sched related stats. I think BPF can provide a great help > there. We have many users in Google that want the kernel to export > various scheduling metrics to userspace. I think BPF is a good fit for > such a task. So one of my recent attempts is to use BPF to account for > the forced idle time caused by core scheduling [1]. This is one of the > topics I want to discuss in my upcoming LPC BPF talk [2]. I guess for profiling we don't necessarily need a dedicated program type etc, but it might be convenient, and some helpers can be useful too. Unfortunately I won't be able to attend your talk, but hopefully I can see it in a record later. I'm very interested. > > Looking forward, I agree that BPF has a great potential in customizing > policies in the scheduler. It has the advantage of quick > experimentation and deployment. One of the use cases I'm thinking of > is to customize load balancing policies. For example, allow using BPF > to influence whether a task can migrate (can_migrate_task). This is > currently only an idea. > > > Our very first experiments with using BPF in CFS look very promising. We're > > at a very early stage, however already have seen a nice latency and ~1% RPS > > wins for our (Facebook's) main web workload. > > > > As I know, Google is working on a more radical approach [2]: they aim to move > > the scheduling code into userspace. It seems that their core motivation is > > somewhat similar: to make the scheduler changes easier to develop, validate > > and deploy. Even though their approach is different, they also use BPF for > > speeding up some hot paths. I think the suggested infrastructure can serve > > their purpose too. > > Yes. Barret can talk more about this, but I think it summarized the > work of ghOSt [3] and the use of BPF in ghOSt well. I took a brief look over how you use BPF in ghOSt and I think what I suggest will work for you as well. I'd appreciate any comments/feedback whether it's definitely true. Thank you! Roman
