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

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>

diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
index 0a6b694..cf34044 100644 (file)
--- a/drivers/ata/ahci.c
+++ b/drivers/ata/ahci.c
@@ -268,6 +268,7 @@ static const struct ata_port_operations ahci_ops = {
 
        .tf_read                = ahci_tf_read,
 
+       .qc_defer               = ata_std_qc_defer,
        .qc_prep                = ahci_qc_prep,
        .qc_issue               = ahci_qc_issue,
 
@@ -298,6 +299,7 @@ static const struct ata_port_operations ahci_vt8251_ops = {
 
        .tf_read                = ahci_tf_read,
 
+       .qc_defer               = ata_std_qc_defer,
        .qc_prep                = ahci_qc_prep,
        .qc_issue               = ahci_qc_issue,
 

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 9467c2f..b666f51 100644 (file)
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -4346,6 +4346,36 @@ int ata_check_atapi_dma(struct ata_queued_cmd *qc)
 }
 
 /**
+ *     ata_std_qc_defer - Check whether a qc needs to be deferred
+ *     @qc: ATA command in question
+ *
+ *     Non-NCQ commands cannot run with any other command, NCQ or
+ *     not.  As upper layer only knows the queue depth, we are
+ *     responsible for maintaining exclusion.  This function checks
+ *     whether a new command @qc can be issued.
+ *
+ *     LOCKING:
+ *     spin_lock_irqsave(host lock)
+ *
+ *     RETURNS:
+ *     ATA_DEFER_* if deferring is needed, 0 otherwise.
+ */
+int ata_std_qc_defer(struct ata_queued_cmd *qc)
+{
+       struct ata_link *link = qc->dev->link;
+
+       if (qc->tf.protocol == ATA_PROT_NCQ) {
+               if (!ata_tag_valid(link->active_tag))
+                       return 0;
+       } else {
+               if (!ata_tag_valid(link->active_tag) && !link->sactive)
+                       return 0;
+       }
+
+       return ATA_DEFER_LINK;
+}
+
+/**
  *     ata_qc_prep - Prepare taskfile for submission
  *     @qc: Metadata associated with taskfile to be prepared
  *
@@ -7111,6 +7141,7 @@ EXPORT_SYMBOL_GPL(ata_interrupt);
 EXPORT_SYMBOL_GPL(ata_do_set_mode);
 EXPORT_SYMBOL_GPL(ata_data_xfer);
 EXPORT_SYMBOL_GPL(ata_data_xfer_noirq);
+EXPORT_SYMBOL_GPL(ata_std_qc_defer);
 EXPORT_SYMBOL_GPL(ata_qc_prep);
 EXPORT_SYMBOL_GPL(ata_dumb_qc_prep);
 EXPORT_SYMBOL_GPL(ata_noop_qc_prep);

diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index dc27400..8ca2cae 100644 (file)
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -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,
@@ -1416,37 +1423,6 @@ static void ata_scsi_qc_complete(struct ata_queued_cmd *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
  *     @cmd: SCSI command to execute
@@ -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;

diff --git a/drivers/ata/sata_nv.c b/drivers/ata/sata_nv.c
index b860f99..40557fe 100644 (file)
--- a/drivers/ata/sata_nv.c
+++ b/drivers/ata/sata_nv.c
@@ -423,6 +423,7 @@ static const struct ata_port_operations nv_adma_ops = {
        .bmdma_start            = ata_bmdma_start,
        .bmdma_stop             = ata_bmdma_stop,
        .bmdma_status           = ata_bmdma_status,
+       .qc_defer               = ata_std_qc_defer,
        .qc_prep                = nv_adma_qc_prep,
        .qc_issue               = nv_adma_qc_issue,
        .freeze                 = nv_adma_freeze,

diff --git a/drivers/ata/sata_sil24.c b/drivers/ata/sata_sil24.c
index d9c010a..9acfce4 100644 (file)
--- a/drivers/ata/sata_sil24.c
+++ b/drivers/ata/sata_sil24.c
@@ -393,6 +393,7 @@ static const struct ata_port_operations sil24_ops = {
 
        .tf_read                = sil24_tf_read,
 
+       .qc_defer               = ata_std_qc_defer,
        .qc_prep                = sil24_qc_prep,
        .qc_issue               = sil24_qc_issue,
 

diff --git a/include/linux/libata.h b/include/linux/libata.h
index c3820f1..b0d4ca0 100644 (file)
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -272,6 +272,10 @@ enum {
        /* ering size */
        ATA_ERING_SIZE          = 32,
 
+       /* return values for ->qc_defer */
+       ATA_DEFER_LINK          = 1,
+       ATA_DEFER_PORT          = 2,
+
        /* desc_len for ata_eh_info and context */
        ATA_EH_DESC_LEN         = 80,
 
@@ -639,6 +643,7 @@ struct ata_port_operations {
 
        void (*data_xfer) (struct ata_device *, unsigned char *, unsigned int, int);
 
+       int (*qc_defer) (struct ata_queued_cmd *qc);
        void (*qc_prep) (struct ata_queued_cmd *qc);
        unsigned int (*qc_issue) (struct ata_queued_cmd *qc);
 
@@ -824,6 +829,7 @@ extern void ata_data_xfer(struct ata_device *adev, unsigned char *buf,
                          unsigned int buflen, int write_data);
 extern void ata_data_xfer_noirq(struct ata_device *adev, unsigned char *buf,
                                unsigned int buflen, int write_data);
+extern int ata_std_qc_defer(struct ata_queued_cmd *qc);
 extern void ata_dumb_qc_prep(struct ata_queued_cmd *qc);
 extern void ata_qc_prep(struct ata_queued_cmd *qc);
 extern void ata_noop_qc_prep(struct ata_queued_cmd *qc);