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

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Date:	Thu, 3 Sep 2009 15:21:23 -0700
From:	Chetan.Loke@...lex.Com
To:	<brking@...ux.vnet.ibm.com>, <akataria@...are.com>
CC:	<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-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.

> -----Original Message-----
> From: linux-kernel-owner@...r.kernel.org [mailto:linux-kernel-
> owner@...r.kernel.org] On Behalf Of Brian King
> Sent: Thursday, September 03, 2009 5:53 PM
> To: akataria@...are.com
> Cc: James Bottomley; Rolf Eike Beer; Matthew Wilcox; Roland Dreier; Bart
> Van Assche; Robert Love; Randy Dunlap; Mike Christie; linux-
> scsi@...r.kernel.org; LKML; Andrew Morton; pv-drivers@...are.com
> Subject: Re: [PATCH] SCSI driver for VMware's virtual HBA - V3.
> 
> Alok Kataria wrote:
> > +
> > +struct pvscsi_adapter {
> > +	char			*mmioBase;
> > +	unsigned int		irq;
> > +	u8			rev;
> > +	bool			use_msi;
> > +	bool			use_msix;
> > +	bool			use_msg;
> > +
> > +	spinlock_t		hw_lock;
> 
> Why not just use host_lock in the scsi_host structure?
> 

Why not an adapter_resource_lock? Why block everyone @ the scsi-mid layer. 

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.

This is the kind of common code that should be provided by the bottom edge of the scsi-layer so that all the scsi-LLDD's can split their tx/rx paths!




> Brian King
> Linux on Power Virtualization
> IBM Linux Technology Center
> 


Chetan
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