linux-kernel - Re: [PATCH RFC v3 3/6] sched/idle: Add a generic poll before enter real idle path

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Message-ID: <20171115121152.gqug5wzerlo3eimd@hirez.programming.kicks-ass.net>
Date:   Wed, 15 Nov 2017 13:11:52 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Quan Xu <quan.xu03@...il.com>
Cc:     kvm@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, x86@...nel.org,
        xen-devel@...ts.xenproject.org,
        Yang Zhang <yang.zhang.wz@...il.com>,
        Quan Xu <quan.xu0@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Kyle Huey <me@...ehuey.com>, Len Brown <len.brown@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Tobias Klauser <tklauser@...tanz.ch>
Subject: Re: [PATCH RFC v3 3/6] sched/idle: Add a generic poll before enter
 real idle path

On Mon, Nov 13, 2017 at 06:06:02PM +0800, Quan Xu wrote:
> From: Yang Zhang <yang.zhang.wz@...il.com>
> 
> Implement a generic idle poll which resembles the functionality
> found in arch/. Provide weak arch_cpu_idle_poll function which
> can be overridden by the architecture code if needed.

No, we want less of those magic hooks, not more.

> Interrupts arrive which may not cause a reschedule in idle loops.
> In KVM guest, this costs several VM-exit/VM-entry cycles, VM-entry
> for interrupts and VM-exit immediately. Also this becomes more
> expensive than bare metal. Add a generic idle poll before enter
> real idle path. When a reschedule event is pending, we can bypass
> the real idle path.

Why not do a HV specific idle driver?