On Jan 31, 2019, at 12:38 PM, Waiman Long [off-list ref] wrote:

On 01/30/2019 10:01 PM, Alex Kogan wrote:

quoted

In CNA, spinning threads are organized in two queues, a main queue for
threads running on the same socket as the current lock holder, and a
secondary queue for threads running on other sockets. For details,
see https://urldefense.proofpoint.com/v2/url?u=https-3A__arxiv.org_abs_1810.05600&d=DwIFaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Hvhk3F4omdCk-GE1PTOm3Kn0A7ApWOZ2aZLTuVxFK4k&m=RdsRU4oU2j-_hNG5kDC5ZEE_XHikl3QLNttCaBde3QU&s=NQ840S1lz53Cq7AnOlPWdnjZI7_Ic3rfYsf-w2aYus4&e=.

Note that this variant of CNA may introduce starvation by continuously
passing the lock to threads running on the same socket. This issue
will be addressed later in the series.

Signed-off-by: Alex Kogan <redacted>
Reviewed-by: Steve Sistare <redacted>

Just wondering if you have tried include PARVIRT_SPINLOCKS option to see
if that patch may screw up the PV qspinlock code.

No, I haven’t yet.
The idea was to make it work for non-PV systems first, and then extend to PV.

Anyway, I do believe your claim that NUMA-aware qspinlock is good for
large systems with many nodes. However, all these extra code are
overhead for small systems that have a single node/socket, for instance.

I will support doing something similar to what had been done to support
PV qspinlock. IOW, a separate slowpath function that can be patched to
become the default depending on the system being run on or a kernel boot
option setting.

I would like to keep the core slowpath function simple and easy to
understand. So most of the CNA code should be encapsulated into some
helper functions and put into a separated file.

Sounds good. 
I think it should be pretty straightforward to encapsulate the CNA code and do what you suggest.
We will look into that.

Thanks,
— Alex

Thanks,
Longman

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