Re: [PATCH 3/3] tcm ibmvscsis driver

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On Mon, 21 Mar 2011 16:13:07 -0700
"Nicholas A. Bellinger" <nab@xxxxxxxxxxxxxxx> wrote:

> On Tue, 2011-03-22 at 08:06 +0900, FUJITA Tomonori wrote:
> > On Mon, 21 Mar 2011 15:34:33 -0700
> > "Nicholas A. Bellinger" <nab@xxxxxxxxxxxxxxx> wrote:
> > 
> > > On Mon, 2011-03-21 at 17:22 -0500, Brian King wrote:
> > > > Tomo,
> > > > 
> > > > Thanks for all the work you've done with this driver. It is much appreciated.
> > > > 
> > > > What sort of performance are you seeing with this? With filebacked devices, I
> > > > was seeing around 1 MB/sec doing a basic disktest run. I haven't compared this
> > > > to ibmvstgt, but I'm pretty sure we did a fair bit better there. Perhaps I've got
> > > > some setup issue?
> > > > 
> > > > I tried a ramdisk device and saw this on the server:
> > > > 
> > > > 
> > > > DMA_TO_DEVICE not supported for RAMDISK_DR with task_sg_chaining=1
> > > > 
> > > > 
> > > 
> > > So for the RAMDISK_DR (direct) SGL memory mapping case we do not support
> > > WRITEs for HW fabric modules using task_sg_changing=1.
> > > 
> > > Please go ahead and use RAMDISK_MCP instead, and I will look at adding a
> > > special case in target_core_fabric_configfs.c code to disallow
> > > RAMDISK_DR symlink creation of configfs ports for target fabric modules
> > > using task_sg_chaining=1.
> > 
> > I really want to remove 'task_sg_chaining=0', all the drivers support
> > sg chaining. It's a hacky. What drivers doesn't support it?
> 
> It's only drivers for which we are not using HW provided scatterlists
> into TCM backend memory, which today is just iscsi_target_mod
> iscsi_target_rx_thread() -> sock_recvmsg() code.

Please fix iscsi_target_mod then.
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