linux-kernel - Re: [PATCH 2/9] KVM: MMU: introduce slot_handle

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Message-ID: <5550A7DA.90800@linux.intel.com>
Date:	Mon, 11 May 2015 21:00:10 +0800
From:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
CC:	gleb@...nel.org, mtosatti@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/9] KVM: MMU: introduce slot_handle_level() and its helper



On 05/07/2015 08:04 PM, Paolo Bonzini wrote:
>
>
> On 30/04/2015 12:24, guangrong.xiao@...ux.intel.com wrote:
>> From: Xiao Guangrong <guangrong.xiao@...ux.intel.com>
>>
>> There are several places walking all rmaps for the memslot so that
>> introduce common functions to cleanup the code
>>
>> Signed-off-by: Xiao Guangrong <guangrong.xiao@...ux.intel.com>
>> ---
>>   arch/x86/kvm/mmu.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 63 insertions(+)
>>
>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>> index ea3e3e4..75a3459 100644
>> --- a/arch/x86/kvm/mmu.c
>> +++ b/arch/x86/kvm/mmu.c
>> @@ -4410,6 +4410,69 @@ void kvm_mmu_setup(struct kvm_vcpu *vcpu)
>>   	init_kvm_mmu(vcpu);
>>   }
>>
>> +/* The return value indicates if tlb flush on all vcpus is needed. */
>> +typedef bool (*slot_level_handler) (struct kvm *kvm, unsigned long *rmap);
>> +
>> +/* The caller should hold mmu-lock before calling this function. */
>> +static bool
>> +slot_handle_level(struct kvm *kvm, struct kvm_memory_slot *memslot,
>> +		  slot_level_handler fn, int min_level, int max_level,
>> +		  bool lock_flush_tlb)
>
> Why not introduce for_each_slot_rmap first, instead of introducing one
> implementation first and then switching to another?  It's a small
> change to reorder the patches like that.

Yes, it's better, will do it in v2.

> I think we should have three
> iterator macros:
>
> #define for_each_rmap_spte(rmap, iter, spte)
>
> #define for_each_slot_rmap(slot, min_level, max_level, iter, rmapp)
>
> #define for_each_slot_rmap_range(slot, iter, min_level, max_level, \
> 				 start_gfn, end_gfn, iter, rmapp)
>
> where the last two take care of initializing the walker/iterator in the
> first part of the "for".

Okay, i agree.

>
> This way, this function would be introduced immediately as this very
> readable code:
>
> 	struct slot_rmap_iterator iter;
> 	unsigned long *rmapp;
> 	bool flush = false;
>
> 	for_each_slot_rmap(memslot, min_level, max_level, &iter, rmapp) {
> 		if (*rmapp)
> 			flush |= fn(kvm, rmapp);
>
> 		if (need_resched() || spin_needbreak(&kvm->mmu_lock)) {
> 			if (flush && lock_flush_tlb) {
> 				kvm_flush_remote_tlbs(kvm);
> 				flush = false;
> 			}
> 			cond_resched_lock(&kvm->mmu_lock);
> 		}
> 	}
>
> 	/*
> 	 * What about adding this here: then callers that pass
> 	 * lock_flush_tlb == true need not care about the return
> 	 * value!
> 	 */
> 	if (flush && lock_flush_tlb) {
> 		kvm_flush_remote_tlbs(kvm);
> 		flush = false;
> 	}
>
> 	return flush;

Good idea.

>
> In addition, some of these functions need to be marked always_inline I
> think; either slot_handle_level/slot_handle_*_level, or the
> iterators/walkers.  Can you collect kvm.ko size for both cases?

After applying patch 1 ~ 5:

no inline:
$ size arch/x86/kvm/kvm.ko
    text    data     bss     dec     hex filename
  366406   51535     473  418414   6626e arch/x86/kvm/kvm.ko

inline:
$ size arch/x86/kvm/kvm.ko
    text    data     bss     dec     hex filename
  366638   51535     473  418646   66356 arch/x86/kvm/kvm.ko

Since there are static functions i prefer allowing GCC automatically
optimizes the code to marking always-inline.

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