linux-kernel - RE: [PATCH] SCSI driver for VMware's virtual HBA

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Date:	Wed, 9 Sep 2009 15:48:38 -0700
From:	Chetan.Loke@...lex.Com
To:	<akataria@...are.com>
CC:	<brking@...ux.vnet.ibm.com>, <James.Bottomley@...e.de>,
	<eike-kernel@...tec.de>, <matthew@....cx>, <rdreier@...co.com>,
	<bvanassche@....org>, <robert.w.love@...el.com>,
	<randy.dunlap@...cle.com>, <michaelc@...wisc.edu>,
	<linux-kernel@...r.kernel.org>, <akpm@...ux-foundation.org>,
	<pv-drivers@...are.com>
Subject: RE: [PATCH] SCSI driver for VMware's virtual HBA - V3.

> -----Original Message-----
> From: Alok Kataria [mailto:akataria@...are.com]
> Sent: Tuesday, September 08, 2009 9:08 PM
> To: Loke,Chetan
> Cc: brking@...ux.vnet.ibm.com; James.Bottomley@...e.de; eike-kernel@sf-
> tec.de; matthew@....cx; rdreier@...co.com; bvanassche@....org;
> robert.w.love@...el.com; randy.dunlap@...cle.com; michaelc@...wisc.edu;
> linux-scsi@...r.kernel.org; linux-kernel@...r.kernel.org; akpm@...ux-
> foundation.org; pv-drivers@...are.com
> Subject: RE: [PATCH] SCSI driver for VMware's virtual HBA - V3.
> 
> Hi Chetan,
> 
> > Alok,
> >
> > (This is just a optimization.You don't need it in order to get your
> > code merged upstream.You can always patch it later on)In fact hw_lock
> > should be split into two locks -
> >
> > req_path_lock(aka tx_lock) and
> > cmpl_path_lock(aka rx_lock).
> >
> > You can then have a full-duplex channel.
> >
> > Revised-code -
> > 	::pvscsi_acquire_context->spin_lock_irqsave(tx_lock)
> > 	::pvscsi_isr->spin_lock_irqsave(rx_lock)
> > 	::some_future_napi_style_pvrx_poll_func->spin_lock_irqsave(rx_lock)
> >
> > 	::for aborts synchronize on the rx_lock so that you know what's
> > completed and what's not.
> >
> 



> I agree about the optimization. Though IMO this will be more attractive
> once we have a device which supports multiple queue pairs.

lpfc driver has native multi-ring support. It won't create hundred's of ring-pairs but the stuff that's present is good enough to start with(at least for this generation).


> Anyways, let me keep this on my plate, I will check how much of an
> benefit this gets us and will decide if this should be done, but as you
> suggested this is for later.
> 

I keep forgetting that this is a pv-driver.So, to reap the benefits of the multi-ring arch, the plumbing should be present in your hypervisor/kernel and NOT in the guest-world.


> Thanks for taking a look.
No worries.


> 
> --Alok


Chetan
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