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    SubjectRe: aim7 scalability issue on 4 socket machine
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    On Thu, 2009-09-17 at 11:35 +0100, Hugh Dickins wrote:
    > On Thu, 17 Sep 2009, Peter Zijlstra wrote:
    > > On Thu, 2009-09-17 at 17:31 +0800, Zhang, Yanmin wrote:
    > > > Aim7 result is bad on my new Nehalem machines (4*8*2 logical cpu). Perf counter
    > > > shows spinlock consumes 70% cpu time on the machine. Lock_stat shows
    > > > anon_vma->lock causes most of the spinlock contention. Function tracer shows
    > > > below call chain creates the spinlock.
    > > >
    > > > do_brk => vma_merge =>vma_adjust
    > > >
    > > > Aim7 consists of lots of subtests. One test is to fork lots of processes and
    > > > every process calls sbrk for 1000 times to grow/shrink the heap. All the vma of
    > > > the heap of all sub-processes point to the same anon_vma and use the same
    > > > anon_vma->lock. When sbrk is called, kernel calls do_brk => vma_merge =>vma_adjust
    > > > and lock anon_vma->lock to create spinlock contentions.
    > > >
    > > > There is a comment section in front of spin_lock(&anon_vma->lock. It says
    > > > anon_vma lock can be optimized when just changing vma->vm_end. As a matter
    > > > of fact, anon_vma->lock is used to protect anon_vma->list when an entry is
    > > > deleted/inserted or the list is accessed. There is no such deletion/insertion
    > > > if only vma->end is changed in function vma_adjust.
    > > >
    > > > Below patch fixes it.
    > > >
    > > > Test results with kernel 2.6.31-rc8. The improvement on the machine is about 150%.
    > >
    > > Did you see Lee's patch?:
    > >
    > > http://lkml.org/lkml/2009/9/9/290
    > >
    > > Added Lee and Hugh to CC, retained the below patch for them.
    >
    > Thanks a lot for the CC, Peter.
    > See my reply to that mail for the slightly corrected version.
    >
    > Yes, Yanmin and Lee appear to be fixing exactly the same issue.
    > I haven't thought through Yanmin's version for correctness, but
    > it lacks the vm_start check I added to Lee's, and I do prefer
    > Lee's style - hey, nothing personal!
    >
    > So, Yanmin, please retest with http://lkml.org/lkml/2009/9/13/25
    > and let us know if that works as well for you - thanks.
    I tested Lee's patch and it does fix the issue.

    Yanmin




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