Re: [Qemu-devel] [PATCH v4 0/2] QOM: object_property_add() performance improvement

["Daniel P. Berrange" <berrange@redhat.com>]

On Tue, Jul 14, 2015 at 12:38:59PM +0300, Pavel Fedin wrote:
> The function originally behaves very badly when adding properties with "[*]"
> suffix. Normally these are used for numbering IRQ pins. In order to find the
> correct starting number the function started from zero and checked for
> duplicates. This takes incredibly long time with large number of CPUs because
> number of IRQ pins on some architectures (like ARM GICv3) gets multiplied by
> number of CPUs.
> 
> The solution is to add one more property which caches last used index so that
> duplication check is not repeated thousands of times. Every time an array is
> expanded the index is picked up from this cache.
> 
> The modification decreases qemu startup time with 32 CPUs by a factor of 2
> (~10 sec vs ~20 sec).

10 seconds to start a QEMU with a mere 32 cpus is still a totally
ridiculous amount of time. Do you know why it is still so slow even
after your suggested patch ? Is it still related to the method
object_property_add(), or are there other areas of code with bad
scalability affecting arm ?

Regards,
Daniel
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