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libsas: remove task_collector mode

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The task_collector mode (or "latency_injector", (C) Dan Willians) is an
optional I/O path in libsas that queues up scsi commands instead of
directly sending it to the hardware.  It generall increases latencies
to in the optiomal case slightly reduce mmio traffic to the hardware.

Only the obsolete aic94xx driver and the mvsas driver allowed to use
it without recompiling the kernel, and most drivers didn't support it
at all.

Remove the giant blob of code to allow better optimizations for scsi-mq
in the future.

Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Hannes Reinecke <[email protected]>
Acked-by: Dan Williams <[email protected]>
This commit is contained in:
Christoph Hellwig 2014-11-05 10:36:28 +01:00
commit 79855d1785
20 changed files with 97 additions and 556 deletions
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82
Documentation/scsi/libsas.txt
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@ -226,9 +226,6 @@ static int register_sas_ha(struct my_sas_ha *my_ha)
my_ha->sas_ha.lldd_dev_found = my_dev_found;
my_ha->sas_ha.lldd_dev_gone = my_dev_gone;
my_ha->sas_ha.lldd_max_execute_num = lldd_max_execute_num; (1)
my_ha->sas_ha.lldd_queue_size = ha_can_queue;
my_ha->sas_ha.lldd_execute_task = my_execute_task;
my_ha->sas_ha.lldd_abort_task = my_abort_task;
@ -247,28 +244,6 @@ static int register_sas_ha(struct my_sas_ha *my_ha)
return sas_register_ha(&my_ha->sas_ha);
}
(1) This is normally a LLDD parameter, something of the
lines of a task collector. What it tells the SAS Layer is
whether the SAS layer should run in Direct Mode (default:
value 0 or 1) or Task Collector Mode (value greater than 1).
In Direct Mode, the SAS Layer calls Execute Task as soon as
it has a command to send to the SDS, _and_ this is a single
command, i.e. not linked.
Some hardware (e.g. aic94xx) has the capability to DMA more
than one task at a time (interrupt) from host memory. Task
Collector Mode is an optional feature for HAs which support
this in their hardware. (Again, it is completely optional
even if your hardware supports it.)
In Task Collector Mode, the SAS Layer would do _natural_
coalescing of tasks and at the appropriate moment it would
call your driver to DMA more than one task in a single HA
interrupt. DMBS may want to use this by insmod/modprobe
setting the lldd_max_execute_num to something greater than
1.
(2) SAS 1.1 does not define I_T Nexus Reset TMF.
Events
@ -325,71 +300,22 @@ PHYE_SPINUP_HOLD -- SATA is present, COMWAKE not sent.
The Execute Command SCSI RPC:
int (*lldd_execute_task)(struct sas_task *, int num,
unsigned long gfp_flags);
int (*lldd_execute_task)(struct sas_task *, gfp_t gfp_flags);
Used to queue a task to the SAS LLDD. @task is the tasks to
be executed. @num should be the number of tasks being
queued at this function call (they are linked listed via
task::list), @gfp_mask should be the gfp_mask defining the
context of the caller.
Used to queue a task to the SAS LLDD. @task is the task to be executed.
@gfp_mask is the gfp_mask defining the context of the caller.
This function should implement the Execute Command SCSI RPC,
or if you're sending a SCSI Task as linked commands, you
should also use this function.
That is, when lldd_execute_task() is called, the command(s)
That is, when lldd_execute_task() is called, the command
go out on the transport *immediately*. There is *no*
queuing of any sort and at any level in a SAS LLDD.
The use of task::list is two-fold, one for linked commands,
the other discussed below.
It is possible to queue up more than one task at a time, by
initializing the list element of struct sas_task, and
passing the number of tasks enlisted in this manner in num.
Returns: -SAS_QUEUE_FULL, -ENOMEM, nothing was queued;
0, the task(s) were queued.
If you want to pass num > 1, then either
A) you're the only caller of this function and keep track
of what you've queued to the LLDD, or
B) you know what you're doing and have a strategy of
retrying.
As opposed to queuing one task at a time (function call),
batch queuing of tasks, by having num > 1, greatly
simplifies LLDD code, sequencer code, and _hardware design_,
and has some performance advantages in certain situations
(DBMS).
The LLDD advertises if it can take more than one command at
a time at lldd_execute_task(), by setting the
lldd_max_execute_num parameter (controlled by "collector"
module parameter in aic94xx SAS LLDD).
You should leave this to the default 1, unless you know what
you're doing.
This is a function of the LLDD, to which the SAS layer can
cater to.
int lldd_queue_size
The host adapter's queue size. This is the maximum
number of commands the lldd can have pending to domain
devices on behalf of all upper layers submitting through
lldd_execute_task().
You really want to set this to something (much) larger than
1.
This _really_ has absolutely nothing to do with queuing.
There is no queuing in SAS LLDDs.
struct sas_task {
dev -- the device this task is destined to
list -- must be initialized (INIT_LIST_HEAD)
task_proto -- _one_ of enum sas_proto
scatter -- pointer to scatter gather list array
num_scatter -- number of elements in scatter