linux-kernel - Re: [RFC PATCH v2 1/7] x86/paravirt: Add pv_idle

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Date:   Wed, 30 Aug 2017 09:33:52 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Yang Zhang <yang.zhang.wz@...il.com>,
        xen-devel@...ts.xensource.com,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        wanpeng.li@...mail.com, mst@...hat.com, pbonzini@...hat.com,
        tglx@...utronix.de, rkrcmar@...hat.com, dmatlack@...gle.com,
        agraf@...e.de, peterz@...radead.org, linux-doc@...r.kernel.org,
        Quan Xu <quan.xu0@...il.com>,
        Jeremy Fitzhardinge <jeremy@...p.org>,
        Chris Wright <chrisw@...s-sol.org>,
        Alok Kataria <akataria@...are.com>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>,
        Kees Cook <keescook@...omium.org>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [RFC PATCH v2 1/7] x86/paravirt: Add pv_idle_ops to paravirt ops

On 29/08/17 15:55, Konrad Rzeszutek Wilk wrote:
> On Tue, Aug 29, 2017 at 11:46:35AM +0000, Yang Zhang wrote:
>> So far, pv_idle_ops.poll is the only ops for pv_idle. .poll is called in
>> idle path which will polling for a while before we enter the real idle
>> state.
>>
>> In virtualization, idle path includes several heavy operations
>> includes timer access(LAPIC timer or TSC deadline timer) which will hurt
>> performance especially for latency intensive workload like message
>> passing task. The cost is mainly come from the vmexit which is a
>> hardware context switch between VM and hypervisor. Our solution is to
>> poll for a while and do not enter real idle path if we can get the
>> schedule event during polling.
>>
>> Poll may cause the CPU waste so we adopt a smart polling mechanism to
>> reduce the useless poll.
>>
>> Signed-off-by: Yang Zhang <yang.zhang.wz@...il.com>
>> Signed-off-by: Quan Xu <quan.xu0@...il.com>
>> Cc: Jeremy Fitzhardinge <jeremy@...p.org>
>> Cc: Chris Wright <chrisw@...s-sol.org>
>> Cc: Alok Kataria <akataria@...are.com>
>> Cc: Rusty Russell <rusty@...tcorp.com.au>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Cc: "H. Peter Anvin" <hpa@...or.com>
>> Cc: x86@...nel.org
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Andy Lutomirski <luto@...nel.org>
>> Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
>> Cc: Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
>> Cc: Kees Cook <keescook@...omium.org>
>> Cc: virtualization@...ts.linux-foundation.org
>> Cc: linux-kernel@...r.kernel.org
> 
> Adding xen-devel.
> 
> Juergen, we really should replace Jeremy's name with xen-devel or
> your name..

I wouldn't mind being added. What does Jeremy think of being removed?

> Wasn't there an patch by you that took some of the 
> mainternship over it?

I added include/linux/hypervisor.h to the PARAVIRT section and offered
to maintain it in case the PARAVIRT maintainers didn't want to.


Juergen