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

[Yang Zhang <yang.zhang.wz@xxxxxxxxx>]

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@xxxxxxxxx>
> > Signed-off-by: Quan Xu <quan.xu0@xxxxxxxxx>
> > Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
> > Cc: Chris Wright <chrisw@xxxxxxxxxxxx>
> > Cc: Alok Kataria <akataria@xxxxxxxxxx>
> > Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> > Cc: x86@xxxxxxxxxx
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> > Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> > Cc: Pan Xinhui <xinhui.pan@xxxxxxxxxxxxxxxxxx>
> > Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> > Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> 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

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