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SubjectRe: [PATCH v2 0/5] Switch arm64 over to qrwlock
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On 10/6/2017 9:34 AM, 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
>
> --->8
>
> Will Deacon (5):
> kernel/locking: Use struct qrwlock instead of struct __qrwlock
> locking/atomic: Add atomic_cond_read_acquire
> kernel/locking: Use atomic_cond_read_acquire when spinning in qrwlock
> arm64: locking: Move rwlock implementation over to qrwlocks
> kernel/locking: Prevent slowpath writers getting held up by fastpath
>
> arch/arm64/Kconfig | 17 ++++
> arch/arm64/include/asm/Kbuild | 1 +
> arch/arm64/include/asm/spinlock.h | 164 +-------------------------------
> arch/arm64/include/asm/spinlock_types.h | 6 +-
> include/asm-generic/atomic-long.h | 3 +
> include/asm-generic/qrwlock.h | 20 +---
> include/asm-generic/qrwlock_types.h | 15 ++-
> include/linux/atomic.h | 4 +
> kernel/locking/qrwlock.c | 83 +++-------------
> 9 files changed, 58 insertions(+), 255 deletions(-)
>

Applied on 4.14-rc4, I tested these patches with multiple combinations of
readers:writers . These patches help prevent writer starvation in every
combination that I tested. Without these patches, when the reader:writer ratio
is 2:1, it's trivial for me to see acquisitions of 250:1 (@ 2R:1W).

After applying the qrwlock patches, I see the acquisition ratios level out to
around ~1.6:1 (@ 2R:1W), which is quite an improvement.

Thanks Will!

Tested-by: Adam Wallis <awallis@codeaurora.org>

--
Adam Wallis
Qualcomm Datacenter Technologies as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.

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