Re: command emulation fix

[Tejun Heo <tj@kernel.org>]

On Thu, Jan 19, 2017 at 03:34:58PM -0500, Tejun Heo wrote:
> Hello, Christoph.
> 
> On Thu, Jan 19, 2017 at 09:27:25PM +0100, Christoph Hellwig wrote:
> > We can move to a small mempool instead.  If we ever want discards
> > (aka TRIM) to perform nicely on ATA a global static buffer isn't
> > going to cut it.  I've spent some time to optimize it for NVMe so
> > that it's usable which I plan to submit soon.  I've not looked ATA
> > in that respect yet, but it's probably going to be an issue.
> 
> So, unless we allocate one mempool per port, we're gonna have to
> synchronize around its use anyway.  mempool can't guarantee allocation
> to multiple users at the same time.  If this is something which
> affects scalability, I'm completley fine with making it per-port (or
> device).  Each ata_port carries 512 byte buffer anyway.  Maybe we can
> reuse that?

But do you actually expect there to be scalability issues around this
buffer?  Its uses are extremely short and libata operations are pretty
strongly synchronized to begin with.

Thanks.

-- 
tejun