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libata-pmp-prep: implement ops->qc_defer()

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Controllers which support PMP have various restrictions on which
combinations of commands are allowed to what number of devices
concurrently.  This patch implements ops->qc_defer() which determines
whether a qc can be issued at the moment or should be deferred.

If the function returns ATA_DEFER_LINK, the qc will be deferred until
a qc completes on the link.  If ATA_DEFER_PORT, until a qc completes
on any link.  The defer conditions are advisory and in general
ATA_DEFER_LINK can be considered as lower priority deferring than
ATA_DEFER_PORT.

ops->qc_defer() replaces fixed ata_scmd_need_defer().  For standard
NCQ/non-NCQ exclusion, ata_std_qc_defer() is implemented.  ahci and
sata_sil24 are converted to use ata_std_qc_defer().

ops->qc_defer() is heavier than the original mechanism because full qc
is prepped before determining to defer it, but various information is
needed to determine defer conditinos and fully translating a qc is the
only way to supply such information in generic manner.

IMHO, this shouldn't cause any noticeable performance issues as

* for most cases deferring occurs rarely (except for NCQ-aware
  cmd-switching PMP)
* translation itself isn't that expensive
* once deferred the command won't be repeated until another command
  completes which usually is a very long time cpu-wise.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
This commit is contained in:
Tejun Heo
2007-09-23 13:14:12 +09:00
committed by Jeff Garzik
parent fb7fd61454
commit 31cc23b349
6 changed files with 67 additions and 36 deletions
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62
drivers/ata/libata-scsi.c
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@@ -749,6 +749,13 @@ static void ata_scsi_sdev_config(struct scsi_device *sdev)
{
sdev->use_10_for_rw = 1;
sdev->use_10_for_ms = 1;
/* Schedule policy is determined by ->qc_defer() callback and
* it needs to see every deferred qc. Set dev_blocked to 1 to
* prevent SCSI midlayer from automatically deferring
* requests.
*/
sdev->max_device_blocked = 1;
}
static void ata_scsi_dev_config(struct scsi_device *sdev,
@@ -1415,37 +1422,6 @@ static void ata_scsi_qc_complete(struct ata_queued_cmd *qc)
ata_qc_free(qc);
}
/**
* ata_scmd_need_defer - Check whether we need to defer scmd
* @dev: ATA device to which the command is addressed
* @is_io: Is the command IO (and thus possibly NCQ)?
*
* NCQ and non-NCQ commands cannot run together. As upper layer
* only knows the queue depth, we are responsible for maintaining
* exclusion. This function checks whether a new command can be
* issued to @dev.
*
* LOCKING:
* spin_lock_irqsave(host lock)
*
* RETURNS:
* 1 if deferring is needed, 0 otherwise.
*/
static int ata_scmd_need_defer(struct ata_device *dev, int is_io)
{
struct ata_link *link = dev->link;
int is_ncq = is_io && ata_ncq_enabled(dev);
if (is_ncq) {
if (!ata_tag_valid(link->active_tag))
return 0;
} else {
if (!ata_tag_valid(link->active_tag) && !link->sactive)
return 0;
}
return 1;
}
/**
* ata_scsi_translate - Translate then issue SCSI command to ATA device
* @dev: ATA device to which the command is addressed
@@ -1477,14 +1453,12 @@ static int ata_scsi_translate(struct ata_device *dev, struct scsi_cmnd *cmd,
void (*done)(struct scsi_cmnd *),
ata_xlat_func_t xlat_func)
{
struct ata_port *ap = dev->link->ap;
struct ata_queued_cmd *qc;
int is_io = xlat_func == ata_scsi_rw_xlat;
int rc;
VPRINTK("ENTER\n");
if (unlikely(ata_scmd_need_defer(dev, is_io)))
goto defer;
qc = ata_scsi_qc_new(dev, cmd, done);
if (!qc)
goto err_mem;
@@ -1508,6 +1482,11 @@ static int ata_scsi_translate(struct ata_device *dev, struct scsi_cmnd *cmd,
if (xlat_func(qc))
goto early_finish;
if (ap->ops->qc_defer) {
if ((rc = ap->ops->qc_defer(qc)))
goto defer;
}
/* select device, send command to hardware */
ata_qc_issue(qc);
@@ -1529,8 +1508,12 @@ err_mem:
return 0;
defer:
ata_qc_free(qc);
DPRINTK("EXIT - defer\n");
return SCSI_MLQUEUE_DEVICE_BUSY;
if (rc == ATA_DEFER_LINK)
return SCSI_MLQUEUE_DEVICE_BUSY;
else
return SCSI_MLQUEUE_HOST_BUSY;
}
/**
@@ -3034,6 +3017,13 @@ int ata_scsi_add_hosts(struct ata_host *host, struct scsi_host_template *sht)
shost->max_channel = 1;
shost->max_cmd_len = 16;
/* Schedule policy is determined by ->qc_defer()
* callback and it needs to see every deferred qc.
* Set host_blocked to 1 to prevent SCSI midlayer from
* automatically deferring requests.
*/
shost->max_host_blocked = 1;
rc = scsi_add_host(ap->scsi_host, ap->host->dev);
if (rc)
goto err_add;