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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:
> 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:// 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
[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?



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