Re: SCSI driver for VMware's virtual HBA - V5.

From: Alok Kataria
Date: Tue Oct 13 2009 - 18:14:38 EST



On Tue, 2009-10-13 at 15:00 -0700, Chris Wright wrote:
> * Alok Kataria (akataria@xxxxxxxxxx) wrote:
> > On Mon, 2009-10-12 at 22:37 -0700, Chris Wright wrote:
> > > > + pvscsi_template.can_queue =
> > > > + min(PVSCSI_MAX_NUM_PAGES_REQ_RING, pvscsi_ring_pages) *
> > > > + PVSCSI_MAX_NUM_REQ_ENTRIES_PER_PAGE;
> > > > + pvscsi_template.cmd_per_lun =
> > > > + min(pvscsi_template.can_queue, pvscsi_cmd_per_lun);
> > >
> > > When/how are these tunables used? Are they still useful?
> >
> > cmd_per_lun, is a commandline parameter.
>
> Actually I meant how is a user supposed to use these? They looked to me
> like tunables that were part of developing a driver that may not be
> needed any longer.
> What are the right values, what are the tradeoffs,
> etc? Or should they just be removed?

The defaults are the right values, and though a normal user won't change
those in practice (he can if he wants to by passing values during
insmod), a developer working on performance tuning can use it.

So I would like to keep these tunables around as it helps any future
performance work.

Thanks,
Alok

>
> thanks,
> -chris

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