linux-kernel - Re: [RFC PATCH 0/4] Scheduler time slice extension

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Message-ID: <41887DDE-453B-482A-83DA-DD95F5C92D34@oracle.com>
Date: Wed, 13 Nov 2024 19:50:37 +0000
From: Prakash Sangappa <prakash.sangappa@...cle.com>
To: Peter Zijlstra <peterz@...radead.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "tglx@...utronix.de"
	<tglx@...utronix.de>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Mathieu
 Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [RFC PATCH 0/4] Scheduler time slice extension



> On Nov 13, 2024, at 10:50 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> On Wed, Nov 13, 2024 at 12:01:22AM +0000, Prakash Sangappa wrote:
> 
>> This patch set implements the above mentioned 50us extension time as posted
>> by Peter. But instead of using restartable sequences as API to set the flag
>> to request the extension, this patch proposes a new API with use of a per
>> thread shared structure implementation described below. This shared structure
>> is accessible in both users pace and kernel. The user thread will set the
>> flag in this shared structure to request execution time extension.
> 
> But why -- we already have rseq, glibc uses it by default. Why add yet
> another thing?

Mainly this provides pinned memory, where kernel can access without the concern of taking a page fault.There could be other use cases in future, where updating user memory in kernel context cannot afford to take pagefaults.  For example implementing  use case like providing the thread state, needs to be done in the context switch path when the thread is going off cpu. 

-Prakash