[sheepdog] [PATCH] sheep: introduce 'short thread' to worker threads

[MORITA Kazutaka]

At Fri, 29 Jun 2012 19:04:18 +0800,
Liu Yuan wrote:
> 
> On 06/29/2012 04:44 PM, MORITA Kazutaka wrote:
> > Does the approach really show better performance and scalability than
> > the current workqueue model with your short thread patch?  I'd like to
> > see the performance number before accepting the change.
> 
> The real benefit is that we don't need pre-set any number of threads,
> because we don't assume cluster nodes number and we just dynamically add
> nodes in on demand. Presetting will for sure constraint cluster
> scalability and statical setting will also waste resource when node is
> not busy. And dynamic threads work on demand and no waste for any
> conditions.
> 
> The performance number is not that relevant:
>   1 it boils down to two pthread call efficient comparison:
> pthread_cond_signal() and pthread_create(), both is heavily affected by
> system resource usage at the time of being calling and kernel's scheduling.
>   2 For a static code review, we can even see that short thread creation
> won't need to hold wi->pending_lock at all and is scheduled to run once
> is created (don't need notification and another lock holding). So I
> think short threads performance might be slightly better than previous
> statically work queue especially for concurrent coherent requests of
> gateway and IO.
> 
> Also we can see that both gateway and io threads exhibit 'on demand'
> characteristics: we need much more threads when system is busy and very
> few when is not, so we need on-demand threads implementation for that too.

Agreed, and applied the patch, thanks.

BTW, should we limit the maximum number of worker threads?  I guess it
causes some problems to run thousands of threads simultaneously.

Thanks,

Kazutaka