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    SubjectRe: [PATCH 7/8] locking: Introduce qrwlock
    On Thu, Feb 13, 2014 at 05:35:46PM +0100, Peter Zijlstra wrote:
    > On Tue, Feb 11, 2014 at 03:12:59PM -0500, Waiman Long wrote:
    > > Using the same locktest program to repetitively take a single rwlock with
    > > programmable number of threads and count their execution times. Each
    > > thread takes the lock 5M times on a 4-socket 40-core Westmere-EX
    > > system. I bound all the threads to different CPUs with the following
    > > 3 configurations:
    > >
    > > 1) Both CPUs and lock are in the same node
    > > 2) CPUs and lock are in different nodes
    > > 3) Half of the CPUs are in same node as the lock & the other half
    > > are remote
    >
    > I can't find these configurations in the below numbers; esp the first is
    > interesting because most computers out there have no nodes.
    >
    > > Two types of qrwlock are tested:
    > > 1) Use MCS lock
    > > 2) Use ticket lock
    >
    > arch_spinlock_t; you forget that if you change that to an MCS style lock
    > this one goes along for free.

    Furthermore; comparing the current rwlock to the ticket-rwlock already
    shows an improvement, so on that aspect its worth it as well.

    And there's also the paravirt people to consider; a fair rwlock will
    make them unhappy; and I'm hoping that their current paravirt ticket
    stuff is sufficient to deal with the ticket-rwlock without them having
    to come and wreck things again.

    Similarly; qspinlock needs paravirt support.




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