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

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Date:   Fri, 1 Sep 2017 14:50:28 +0800
From:   Yang Zhang <yang.zhang.wz@...il.com>
To:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        xen-devel@...ts.xensource.com, jgross@...e.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 2017/8/29 21:55, 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.. Wasn't there an patch by you that took some of the
> mainternship over it?

Hi Konard, I didn't test it in Xen side since i don't have the 
environment but i can add it for Xen in next version if you think it is 
useful to Xen as well.

> 
>> ---
>>   arch/x86/include/asm/paravirt.h       | 5 +++++
>>   arch/x86/include/asm/paravirt_types.h | 6 ++++++
>>   arch/x86/kernel/paravirt.c            | 6 ++++++
>>   3 files changed, 17 insertions(+)
>>
>> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
>> index 9ccac19..6d46760 100644
>> --- a/arch/x86/include/asm/paravirt.h
>> +++ b/arch/x86/include/asm/paravirt.h
>> @@ -202,6 +202,11 @@ static inline unsigned long long paravirt_read_pmc(int counter)
>>   
>>   #define rdpmcl(counter, val) ((val) = paravirt_read_pmc(counter))
>>   
>> +static inline void paravirt_idle_poll(void)
>> +{
>> +	PVOP_VCALL0(pv_idle_ops.poll);
>> +}
>> +
>>   static inline void paravirt_alloc_ldt(struct desc_struct *ldt, unsigned entries)
>>   {
>>   	PVOP_VCALL2(pv_cpu_ops.alloc_ldt, ldt, entries);
>> diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
>> index 9ffc36b..cf45726 100644
>> --- a/arch/x86/include/asm/paravirt_types.h
>> +++ b/arch/x86/include/asm/paravirt_types.h
>> @@ -324,6 +324,10 @@ struct pv_lock_ops {
>>   	struct paravirt_callee_save vcpu_is_preempted;
>>   } __no_randomize_layout;
>>   
>> +struct pv_idle_ops {
>> +	void (*poll)(void);
>> +} __no_randomize_layout;
>> +
>>   /* This contains all the paravirt structures: we get a convenient
>>    * number for each function using the offset which we use to indicate
>>    * what to patch. */
>> @@ -334,6 +338,7 @@ struct paravirt_patch_template {
>>   	struct pv_irq_ops pv_irq_ops;
>>   	struct pv_mmu_ops pv_mmu_ops;
>>   	struct pv_lock_ops pv_lock_ops;
>> +	struct pv_idle_ops pv_idle_ops;
>>   } __no_randomize_layout;
>>   
>>   extern struct pv_info pv_info;
>> @@ -343,6 +348,7 @@ struct paravirt_patch_template {
>>   extern struct pv_irq_ops pv_irq_ops;
>>   extern struct pv_mmu_ops pv_mmu_ops;
>>   extern struct pv_lock_ops pv_lock_ops;
>> +extern struct pv_idle_ops pv_idle_ops;
>>   
>>   #define PARAVIRT_PATCH(x)					\
>>   	(offsetof(struct paravirt_patch_template, x) / sizeof(void *))
>> diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
>> index bc0a849..1b5b247 100644
>> --- a/arch/x86/kernel/paravirt.c
>> +++ b/arch/x86/kernel/paravirt.c
>> @@ -128,6 +128,7 @@ static void *get_call_destination(u8 type)
>>   #ifdef CONFIG_PARAVIRT_SPINLOCKS
>>   		.pv_lock_ops = pv_lock_ops,
>>   #endif
>> +		.pv_idle_ops = pv_idle_ops,
>>   	};
>>   	return *((void **)&tmpl + type);
>>   }
>> @@ -312,6 +313,10 @@ struct pv_time_ops pv_time_ops = {
>>   	.steal_clock = native_steal_clock,
>>   };
>>   
>> +struct pv_idle_ops pv_idle_ops = {
>> +	.poll = paravirt_nop,
>> +};
>> +
>>   __visible struct pv_irq_ops pv_irq_ops = {
>>   	.save_fl = __PV_IS_CALLEE_SAVE(native_save_fl),
>>   	.restore_fl = __PV_IS_CALLEE_SAVE(native_restore_fl),
>> @@ -471,3 +476,4 @@ struct pv_mmu_ops pv_mmu_ops __ro_after_init = {
>>   EXPORT_SYMBOL    (pv_mmu_ops);
>>   EXPORT_SYMBOL_GPL(pv_info);
>>   EXPORT_SYMBOL    (pv_irq_ops);
>> +EXPORT_SYMBOL    (pv_idle_ops);
>> -- 
>> 1.8.3.1
>>


-- 
Yang
Alibaba Cloud Computing