lkml.org 
[lkml]   [2012]   [Apr]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 00/13] KVM: MMU: fast page fault
    On 04/15/2012 05:32 PM, Avi Kivity wrote:

    > On 04/13/2012 05:25 PM, Takuya Yoshikawa wrote:
    >> I forgot to say one important thing -- I might give you wrong impression.
    >>
    >> I am perfectly fine with your lock-less work. It is really nice!
    >>
    >> The reason I say much about O(1) is that O(1) and rmap based
    >> GET_DIRTY_LOG have fundamentally different characteristics.
    >>
    >> I am thinking really seriously how to make dirty page tracking work
    >> well with QEMU in the future.
    >>
    >> For example, I am thinking about multi-threaded and fine-grained
    >> GET_DIRTY_LOG.
    >>
    >> If we use rmap based GET_DIRTY_LOG, we can restrict write protection to
    >> only a selected area of one guest memory slot.
    >>
    >> So we may be able to make each thread process dirty pages independently
    >> from other threads by calling GET_DIRTY_LOG for its own area.
    >>
    >> But I know that O(1) has its own good point.
    >> So please wait a bit. I will write up what I am thinking or send patches.
    >>
    >> Anyway, I am looking forward to your lock-less work!
    >> It will improve the current GET_DIRTY_LOG performance.
    >>
    >>
    >
    > Just to throw another idea into the mix - we can have write-protect-less
    > dirty logging, too. Instead of write protection, drop the dirty bit,
    > and check it again when reading the dirty log. It might look like we're
    > accessing the spte twice here, but it's actually just once - when we
    > check it to report for GET_DIRTY_LOG call N, we also prepare it for call
    > N+1.
    >


    Walking all gfn's rmap is still expensive, at least, it is not good for
    the scalability.

    I want to use a generation number to notify mmu write-protect the PML4s.
    It is complete out of mmu-lock and comparing lockless write enabling can
    let it rungs as parallel as possible.



    \
     
     \ /
      Last update: 2012-04-17 08:23    [W:3.753 / U:0.428 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site