Re: [PATCH v4] drivers/block/mtip32xx: Adding new driver mtip32xx

[Eric Seppanen]

On Tue, Sep 13, 2011 at 5:49 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> Btw, there is another _huge_ issue with the driver, and that is the
> lack of any internal queueing.  Remember the make_request interface is
> an extremly thin layer (or rather the lack of it) below the filesystem.
>
> So for example if eh_active is non-zero you return -EBUSY to the
> filesystems.  That's an error code it a) doesn't recognize and b)
> couldn't handle even if it did.  Similarly mtip_hw_get_scatterlist
> simply blocks if no tag is currently available instead of queueing
> it up.

Just out of curiosity, why is blocking on no-tag-available a bad
thing?  How is it any different than the blocking that will occur when
a request queue is full?  When the hardware queue depth is bigger than
that of a request queue, what extra benefit does queuing give?
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