linux-kernel - Re: SCSI driver for VMware's virtual HBA

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Message-Id: <1255471981.12792.126.camel@ank32.eng.vmware.com>
Date:	Tue, 13 Oct 2009 15:13:01 -0700
From:	Alok Kataria <akataria@...are.com>
To:	Chris Wright <chrisw@...s-sol.org>
Cc:	James Bottomley <James.Bottomley@...e.de>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Mike Christie <michaelc@...wisc.edu>,
	Bart Van Assche <bvanassche@....org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	Matthew Wilcox <matthew@....cx>,
	"pv-drivers@...are.com" <pv-drivers@...are.com>,
	Roland Dreier <rdreier@...co.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Chetan.Loke@...lex.Com" <Chetan.Loke@...lex.Com>,
	Brian King <brking@...ux.vnet.ibm.com>,
	Rolf Eike Beer <eike-kernel@...tec.de>,
	Robert Love <robert.w.love@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Walker <dwalker@...o99.com>, Greg KH <gregkh@...e.de>,
	"virtualization@...ts.linux-foundataion.org" 
	<virtualization@...ts.linux-foundataion.org>
Subject: Re: SCSI driver for VMware's virtual HBA - V5.


On Tue, 2009-10-13 at 15:00 -0700, Chris Wright wrote:
> * Alok Kataria (akataria@...are.com) 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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