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

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Message-ID: <20250205161945.44daf018@gandalf.local.home>
Date: Wed, 5 Feb 2025 16:19:45 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Prakash Sangappa <prakash.sangappa@...cle.com>
Cc: Joel Fernandes <joel@...lfernandes.org>, Peter Zijlstra
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Subject: Re: [RFC][PATCH 1/2] sched: Extended scheduler time slice

On Wed, 5 Feb 2025 21:08:47 +0000
Prakash Sangappa <prakash.sangappa@...cle.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.

I agree with Peter about not caring about system calls. If you can do a
system call in a critical path, then just use futexes.

The only reason I support system calls is for debugging. That's because I
write into the trace_marker from user space to see if things are working,
and that requires a system call. But once things are working, I'll make it
not work for system calls too.

-- Steve