Re: Performance problem about address translation

[xinyue <xinyue@nfs.iscas.ac.cn>]

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	在 2015-07-06, Mon, 16:11:02 ,Andrew Cooper 写到：


	
		On 06/07/2015 08:58, xinyue wrote:
	
		 



	
		
			
			
			
			在 2015-07-06, Mon, 15:44:53 ,Andrew Cooper 写到：
			
				On 06/07/2015 08:22, xinyue wrote:
			
				 
			
				
					Hi,
					
					    For I want to translate the virtual address in HVM DomU to virtual address in Xen. But when I use the function paging_gva_to_gfn and get_gfn, I can feel the performance down quickly, the machine become very hot and then I have to force the machine shutting down.
					
			
			
			Your machine clearly isn't cooled sufficiently, which is the first problem.
			
			
				
					
					The codes I used as below:
					    uint32_t pfec = PFEC_page_present;
					    unsigned long gfn;
					    unsigned long mfn;
					    unsigned long virtaddr;
					    struct vcpu *vcpu = current;
					    struct domain *d = vcpu->domain;
					    p2m_type_t t;
					
					    gfn = paging_gva_to_gfn(current, 0xc0290000, &pfec);
					    mfn = get_gfn(d, gfn, &t);
					    virtaddr = map_domain_page(mfn_x(mfn));
					
					I also use the dbg_hvm_va2mfn function in debug.c, performance problem still present.
					
			
			
			Walking pagetables in software is slow.  There is no getting around this.
			
			Your performance problems will be caused by performing the operation far too often.  You should find a way to reduce this.
			
			
			
			
			Thanks very much, I think I only do this for just once. And after the thanslation is done, the performance is not turn to normal. Does that mean that if I wait long enough it will recovery?
	
	
	It almost certainly means you are not doing it just once like you suppose.
	
	~andrew    
	
	    Yes, you are right. I added printk in get_gfn and found it was call many times. I'll check why that happens. Thanks a lot!
	
	Sorry for mistaking it, the calls of these functions in log appear before I invoke them. These functions that I invoked are through hypercall in HVM DomU, through the log I think I invoked them only once. Maybe the performance problem is caused by the parameters I used? Could you help me the check if I used them unproperly as posted before.
	
	Another question is when I add printk in paging_gva_to gfn function, the performance alse down serioursly that it can't even boot hvm domu successfully. I am wondering why.
	
	Thanks again and best regards!
	
	
	xinyue


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