Re: [Qemu-devel] [PATCH v5 13/18] qht: support parallel writes

[Emilio G. Cota]

On Wed, May 25, 2016 at 01:17:21 +0300, Sergey Fedorov wrote:
> >> With this implementation we could:
> >>  (1) get rid of qht_map::stale
> >>  (2) don't waste cycles waiting for resize to complete
> > I'll include this in v6.
> 
> How is it by perf?

Not much of a difference, since resize is a slow path. Calling
qht-bench with lots of update and resize threads performs very
poorly either way =D

I like the change though because using the mutex here simplifies
the resize code; there's no guilt anymore attached to holding the lock
for some time (e.g. when allocating a new, possible quite large,
map), whereas with the spinlock we would allocate it before
acquiring the lock, without knowing whether the allocation would
be needed in the end.

                Emilio