Messages in this thread |  | | Date | Mon, 9 Oct 2017 00:30:52 +0300 | From | Yury Norov <> | Subject | Re: [PATCH v2 0/5] Switch arm64 over to qrwlock |
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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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