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    SubjectRe: [PATCH v2 0/5] Switch arm64 over to qrwlock
    On Fri, Oct 06, 2017 at 02:34:37PM +0100, Will Deacon wrote:
    > Hi all,
    >
    > This is version two of the patches I posted yesterday:
    >
    > http://lists.infradead.org/pipermail/linux-arm-kernel/2017-October/534666.html
    >
    > I'd normally leave it longer before posting again, but Peter had a good
    > suggestion to rework the layout of the lock word, so I wanted to post a
    > version that follows that approach.
    >
    > I've updated my branch if you're after the full patch stack:
    >
    > git://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git qrwlock
    >
    > As before, all comments (particularly related to testing and performance)
    > welcome!
    >
    > Cheers,
    >
    > Will

    Hi Will,

    I tested your patches with locktorture and found measurable performance
    regression. I also respin the patch of Jan Glauber [1], and I also
    tried Jan's patch with patch 5 from this series. Numbers differ a lot
    from my previous measurements, but since that I changed working
    station and use qemu with the support of parallel threads.
    Spinlock Read-RW lock Write-RW lock
    Vanilla: 129804626 12340895 14716138
    This series: 113718002 10982159 13068934
    Jan patch: 117977108 11363462 13615449
    Jan patch + #5: 121483176 11696728 13618967

    The bottomline of discussion [1] was that queued locks are more
    effective when SoC has many CPUs. And 4 is not many. My measurement
    was made on the 4-CPU machine, and it seems it confirms that. Does
    it make sense to make queued locks default for many-CPU machines only?

    There were 2 preparing patches in the series:
    [PATCH 1/3] kernel/locking: #include <asm/spinlock.h> in qrwlock
    and
    [PATCH 2/3] asm-generic: don't #include <linux/atomic.h> in qspinlock_types.h

    1st patch is not needed anymore because Babu Moger submitted similar patch that
    is already in mainline: 9ab6055f95903 ("kernel/locking: Fix compile error with
    qrwlock.c"). Could you revisit second patch?

    [1] https://lkml.org/lkml/2017/5/3/330

    Yury

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