[PATCH v10 0/9] Hyper-V: paravirtualized remote TLB flushing and hypercall improvements

Wanpeng Li kernellwp at gmail.com
Mon Nov 6 11:07:28 UTC 2017

2017-11-06 18:10 GMT+08:00 Vitaly Kuznetsov <vkuznets at redhat.com>:
> Wanpeng Li <kernellwp at gmail.com> writes:
>> 2017-11-06 17:14 GMT+08:00 Vitaly Kuznetsov <vkuznets at redhat.com>:
>>> Wanpeng Li <kernellwp at gmail.com> writes:
>>>> 2017-08-03 0:09 GMT+08:00 Vitaly Kuznetsov <vkuznets at redhat.com>:
>>>>> Changes since v9:
>>>>> - Rebase to 4.13-rc3.
>>>>> - Drop PATCH1 as it was already taken by Greg to char-misc tree. There're no
>>>>>   functional dependencies on this patch so the series can go through a different tree
>>>>>   (and it actually belongs to x86 if I got Ingo's comment right).
>>>>> - Add in missing void return type in PATCH1 [Colin King, Ingo Molnar, Greg KH]
>>>>> - A few minor fixes in what is now PATCH7: add pr_fmt, tiny style fix in
>>>>>   hyperv_flush_tlb_others() [Andy Shevchenko]
>>>>> - Fix "error: implicit declaration of function 'virt_to_phys'" in PATCH2
>>>>>   reported by kbuild test robot (#include <asm/io.h>)
>>>>> - Add Steven's 'Reviewed-by:' to PATCH9.
>>>>> Original description:
>>>>> Hyper-V supports hypercalls for doing local and remote TLB flushing and
>>>>> gives its guests hints when using hypercall is preferred. While doing
>>>>> hypercalls for local TLB flushes is probably not practical (and is not
>>>>> being suggested by modern Hyper-V versions) remote TLB flush with a
>>>>> hypercall brings significant improvement.
>>>>> To test the series I wrote a special 'TLB trasher': on a 16 vCPU guest I
>>>>> was creating 32 threads which were doing 100000 mmap/munmaps each on some
>>>>> big file. Here are the results:
>>>>> Before:
>>>>> # time ./pthread_mmap ./randfile
>>>>> real    3m33.118s
>>>>> user    0m3.698s
>>>>> sys     3m16.624s
>>>>> After:
>>>>> # time ./pthread_mmap ./randfile
>>>>> real    2m19.920s
>>>>> user    0m2.662s
>>>>> sys     2m9.948s
>>>>> This series brings a number of small improvements along the way: fast
>>>>> hypercall implementation and using it for event signaling, rep hypercalls
>>>>> implementation, hyperv tracing subsystem (which only traces the newly added
>>>>> remote TLB flush for now).
>>>> Hi Vitaly,
>>>> Could you attach your benchmark? I'm interested in to try the
>>>> implementation in paravirt kvm.
>>> Oh, this would be cool) I briefly discussed the idea with Radim (one of
>>> KVM maintainers) during the last KVM Forum and he wasn't opposed to the
>>> idea. Need to talk to Paolo too. Good thing is that we have everything
>> I talk with Paolo today and he points this feature to me, so I believe
>> he likes it. :) In addition,
>> https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/reference/tlfs
>> I search Hypervisor Top Level Functional Specification v5.0b.pdf
>> document but didn't find a section introduce the Hyper-V:
>> paravirtualized remote TLB flushing and hypercall stuff, could you
>> point out?
> It's there, search for
> HvFlushVirtualAddressSpace/HvFlushVirtualAddressSpaceEx and
> HvFlushVirtualAddressList/HvFlushVirtualAddressListEx.

Got it, thanks.

Wanpeng Li

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