Re: [PATCH] kvmtool: Add parameter to specifiy number of threads in thread_pool

[Andreas Herrmann <andreas.herrmann@caviumnetworks.com>]

On Mon, Jun 29, 2015 at 10:45:03AM +0100, Will Deacon wrote:
> On Mon, Jun 29, 2015 at 08:45:44AM +0100, Andreas Herrmann wrote:
> > 
> > With current code the number of threads added to the thread_pool
> > equals number of online CPUs. Thus on an OcteonIII cn78xx system we
> > usually have 48 threads per guest just for the thread_pool. IMHO this
> > is overkill for guests that just have a few vCPUs and/or if a guest is
> > pinned to a subset of host CPUs. E.g.
> > 
> >  # numactl -C 4,5,7,8 ./lkvm run -c 2 -m 256 -k paravirt -d rootfs.ext3 ...
> >  # ps -La | grep threadpool-work | wc -l
> >  48
> > 
> > Don't change default behaviour (for sake of compatibility) but
> > introduce a new parameter ("-t" or "--threads") that allows to specify
> > number of threads to be created for the thread_pool:
> > 
> >  # numactl -C 4,5,7,8 ./lkvm run -c 2 -m 256 --threads 4 -k paravirt -d ...
> >  # ps -La | grep threadpool-work | wc -l
> >  4
> 
> We should probably bound this on some minimum value. I assume things go
> pear-shaped if you pass --threads 1 (or 0, or -1)?

Ouch, yes, range must be checked (esp. for -1).

I think the passed value should be in [1, number of online CPUs].


Andreas