Keir,
Would you consider the middle approach (tools + normal p2m code) for
3.4? I understand that 1GB PoD is too big. But the middle one is much
simpler.
Thanks,
-Wei
-----Original Message-----
From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
Sent: Wednesday, March 18, 2009 12:33 PM
To: George Dunlap; Huang2, Wei
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx; Tim Deegan
Subject: Re: [Xen-devel] [RFC][Patches] Xen 1GB Page Table Support
I'm not sure about putting this in for 3.4 unless there's a significant
performance win.
-- Keir
On 18/03/2009 17:20, "George Dunlap" <George.Dunlap@xxxxxxxxxxxxx>
wrote:
> Thanks for doing this work, Wei -- especially all the extra effort for
> the PoD integration.
>
> One question: How well would you say you've tested the PoD
> functionality? Or to put it the other way, how much do I need to
> prioritize testing this before the 3.4 release?
>
> It wouldn't be a bad idea to do as you suggested, and break things
> into 2 meg pages for the PoD case. In order to take the best
> advantage of this in a PoD scenario, you'd need to have a balloon
> driver that could allocate 1G of continuous *guest* p2m space, which
> seems a bit optimistic at this point...
>
> -George
>
> 2009/3/18 Huang2, Wei <Wei.Huang2@xxxxxxx>:
>> Current Xen supports 2MB super pages for NPT/EPT. The attached
patches
>> extend this feature to support 1GB pages. The PoD
(populate-on-demand)
>> introduced by George Dunlap made P2M modification harder. I tried to
>> preserve existing PoD design by introducing a 1GB PoD cache list.
>>
>>
>>
>> Note that 1GB PoD can be dropped if we don't care about 1GB when PoD
is
>> enabled. In this case, we can just split 1GB PDPE into 512x2MB PDE
entries
>> and grab pages from PoD super list. That can pretty much make
>> 1gb_p2m_pod.patch go away.
>>
>>
>>
>> Any comment/suggestion on design idea will be appreciated.
>>
>>
>>
>> Thanks,
>>
>>
>>
>> -Wei
>>
>>
>>
>>
>>
>> The following is the description:
>>
>> === 1gb_tools.patch ===
>>
>> Extend existing setup_guest() function. Basically, it tries to
allocate 1GB
>> pages whenever available. If this request fails, it falls back to
2MB. If
>> both fail, then 4KB pages will be used.
>>
>>
>>
>> === 1gb_p2m.patch ===
>>
>> * p2m_next_level()
>>
>> Check PSE bit of L3 page table entry. If 1GB is found (PSE=1), we
split 1GB
>> into 512 2MB pages.
>>
>>
>>
>> * p2m_set_entry()
>>
>> Configure the PSE bit of L3 P2M table if page order == 18 (1GB).
>>
>>
>>
>> * p2m_gfn_to_mfn()
>>
>> Add support for 1GB case when doing gfn to mfn translation. When L3
entry is
>> marked as POPULATE_ON_DEMAND, we call 2m_pod_demand_populate().
Otherwise,
>> we do the regular address translation (gfn ==> mfn).
>>
>>
>>
>> * p2m_gfn_to_mfn_current()
>>
>> This is similar to p2m_gfn_to_mfn(). When L3 entry s marked as
>> POPULATE_ON_DEMAND, it demands a populate using
p2m_pod_demand_populate().
>> Otherwise, it does a normal translation. 1GB page is taken into
>> consideration.
>>
>>
>>
>> * set_p2m_entry()
>>
>> Request 1GB page
>>
>>
>>
>> * audit_p2m()
>>
>> Support 1GB while auditing p2m table.
>>
>>
>>
>> * p2m_change_type_global()
>>
>> Deal with 1GB page when changing global page type.
>>
>>
>>
>> === 1gb_p2m_pod.patch ===
>>
>> * xen/include/asm-x86/p2m.h
>>
>> Minor change to deal with PoD. It separates super page cache list
into 2MB
>> and 1GB lists. Similarly, we record last gpfn of sweeping for both
2MB and
>> 1GB.
>>
>>
>>
>> * p2m_pod_cache_add()
>>
>> Check page order and add 1GB super page into PoD 1GB cache list.
>>
>>
>>
>> * p2m_pod_cache_get()
>>
>> Grab a page from cache list. It tries to break 1GB page into 512 2MB
pages
>> if 2MB PoD list is empty. Similarly, 4KB can be requested from super
pages.
>> The breaking order is 2MB then 1GB.
>>
>>
>>
>> * p2m_pod_cache_target()
>>
>> This function is used to set PoD cache size. To increase PoD target,
we try
>> to allocate 1GB from xen domheap. If this fails, we try 2MB. If both
fail,
>> we try 4KB which is guaranteed to work.
>>
>>
>>
>> To decrease the target, we use a similar approach. We first try to
free 1GB
>> pages from 1GB PoD cache list. If such request fails, we try 2MB PoD
cache
>> list. If both fail, we try 4KB list.
>>
>>
>>
>> * p2m_pod_zero_check_superpage_1gb()
>>
>> This adds a new function to check for 1GB page. This function is
similar to
>> p2m_pod_zero_check_superpage_2mb().
>>
>>
>>
>> * p2m_pod_zero_check_superpage_1gb()
>>
>> We add a new function to sweep 1GB page from guest memory. This is
the same
>> as p2m_pod_zero_check_superpage_2mb().
>>
>>
>>
>> * p2m_pod_demand_populate()
>>
>> The trick of this function is to do remap_and_retry if
p2m_pod_cache_get()
>> fails. When p2m_pod_get() fails, this function will splits p2m table
entry
>> into smaller ones (e.g. 1GB ==> 2MB or 2MB ==> 4KB). That can
guarantee
>> populate demands always work.
>>
>>
>>
>>
>>
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@xxxxxxxxxxxxxxxxxxx
>> http://lists.xensource.com/xen-devel
>>
>>
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