Re: [RFC PATCH v2 1/7] x86/paravirt: Add pv_idle_ops to paravirt ops

Yang Zhang
2017-09-01T06:54:29Z

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@gmail.com>
>> Signed-off-by: Quan Xu <quan.xu0@gmail.com>
>> Cc: Jeremy Fitzhardinge <jeremy@goop.org>
>> Cc: Chris Wright <chrisw@sous-sol.org>
>> Cc: Alok Kataria <akataria@vmware.com>
>> Cc: Rusty Russell <rusty@rustcorp.com.au>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Cc: Ingo Molnar <mingo@redhat.com>
>> Cc: "H. Peter Anvin" <hpa@zytor.com>
>> Cc: x86@kernel.org
>> Cc: Peter Zijlstra <peterz@infradead.org>
>> Cc: Andy Lutomirski <luto@kernel.org>
>> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>> Cc: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
>> Cc: Kees Cook <keescook@chromium.org>
>> Cc: virtualization@lists.linux-foundation.org
>> Cc: linux-kernel@vger.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