Re: Performance problem about address translation

[Andrew Cooper <andrew.cooper3@citrix.com>]

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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;
>>
>>     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

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