[stgt] [PATCH 1/3] NOT_LAST bit in cmd state, enables batch submission

[FUJITA Tomonori]

On Mon, 7 Nov 2011 17:09:57 +0200
Alexander Nezhinsky <alexandern at mellanox.com> wrote:

> To enable submitting batches of scsi commands by the backing stores,
> NOT_LAST bit is added to the command state.
> This integrates the batching feature seamlessly both for the LLDs and the
> backing stores:
> - the backing stores not supporting batched mode can safely disregard NOT_LAST
>   bit and submit all commands separately (as previously);
> - the LLDs can also ignore the bit and not set it at all, as the default
>   value NOT_LAST=0 means that each command is "last" (i.e. separately submitted,
>   in this context), so that even the backing stores which do support batching
>   will make no attempt to batch it.
> - when both LLD and BS support batching, the LLDs which accumulate scsi cmds
>   may submit them marking all but the last one with NOT_LAST=1. The BS is
>   hinted to queue the commands marked  with NOT_LAST=1 until a command marked
>   NOT_LAST=0 is submitted, then all the commands previously queued can
>   be submitted, if approppriate. The NOT_LAST=0 bit only instructs the BS that
>   the currently available batch is complete, so that more commands may
>   not arrive for quite a long time, but the BS may decide to actually
>   separate or combine these "batches" according to its own algorithms.
> 
> Signed-off-by: Alexander Nezhinsky <alexandern at mellanox.com>
> ---
>  usr/scsi_cmnd.h |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)

All applied, thanks!
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