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Re: Best practice for new linux block driver device naming?

From: Lennart Sorensen
Subject: Re: Best practice for new linux block driver device naming?
Date: Fri, 8 Mar 2013 17:49:11 -0500
User-agent: Mutt/1.5.20 (2009-06-14)

On Fri, Mar 08, 2013 at 04:34:28PM -0600, address@hidden wrote:
> I get ~4x the IOPSs with a block driver vs. scsi driver due to contention
> for locks in the scsi mid layer (in scsi_request_fn).  It's the
> difference between the device being worth manufacturing vs. not.

Well that starts to qualify as a good reason I suppose.  Of course it
also makes you wonder if perhaps some work on optimizing that part of
the scsi stack is oin order (I have no idea if that's even plausible).

> See this thread:
> Driver is similar to nvme (also a new block driver), but this one is
> for SCSI over PCIe, basically highly parallelized access to very low
> latency devices and trying to use the SCSI midlayer kills the IOPS.

Some nifty hardware that's for sure.

> There were reasons back then for doing that one as a block driver
> which are no longer extant (hence the existence of the hpsa driver
> which supplanted cciss for new smart array devices.)
> All other things being equal, I would also prefer a scsi driver.
> Heck, it's called SCSI over PCIe -- I tried like hell to get it 
> to perform adequately as a SCSI driver but all other things are
> not equal, not even close, the block driver was ~4x as fast.
> So we reluctantly go with a block driver, just like nvme did.

Makes sense.  Perhaps that does mean having to teach grub about it then.

Len Sorensen

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