Re: [RFC][PATCH 1/2] sched: Extended scheduler time slice

[Steven Rostedt <rostedt@goodmis.org>]

On Wed, 5 Feb 2025 16:19:45 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Wed, 5 Feb 2025 21:08:47 +0000
> Prakash Sangappa <prakash.sangappa@oracle.com> wrote:
> 
> > The new syscall/API proposed was to provide per thread shared mapped 
> > area(shared structure) that are allocated from memory pages that are pinned. 
> > So the kernel could access it without the need for a copyin/copyout. 
> > 
> > The idea is that it would be helpful in places where we cannot take a page 
> > fault in the kernel codepath.  
> 
> What places do we need to decided this in a critical path? If we follow my
> proposal, where we set NEED_RESCHED_LAZY on sched_tick when it interrupts
> user space, then it should all work out.

Actually, it doesn't need to be pinned for kernel critical paths (like an
interrupt handler). That's because when entering the user critical path, it
writes to the location, which will fault that memory in. If the page isn't
there when the kernel accesses it, it most likely means the task isn't in a
critical section and there's no reason to extend the tick.

-- Steve