On Fri, 15 Dec 2017, Vainikka Tuomas wrote:
> Hello,
>
> Just bear in mind that there was no need for the PIO transfers when the
> TCQ was hacked off. Commands over DMA worked fine then at least on my
> Blizzard SCSI-IV...
Inhibiting TCQ also affects performance.
If you want to, you can measure the difference (compared to Michael's
patch) by using a patch like the one below, with the option
esp_scsi.esp_no_tcq=1.
The use of PIO for short transfers should cost nothing in the absence of
TCQ because there should be no short tranfers.
--
>
> -Tuomas
>
diff --git a/drivers/scsi/esp_scsi.c b/drivers/scsi/esp_scsi.c
index c3fc34b9964d..69c3de96b79c 100644
--- a/drivers/scsi/esp_scsi.c
+++ b/drivers/scsi/esp_scsi.c
@@ -37,6 +37,8 @@
/* SCSI bus reset settle time in seconds. */
static int esp_bus_reset_settle = 3;
+static int esp_no_tcq = -1;
+
static u32 esp_debug;
#define ESP_DEBUG_INTR 0x00000001
#define ESP_DEBUG_SCSICMD 0x00000002
@@ -698,7 +700,7 @@ static struct esp_cmd_entry
*find_and_prep_issuable_command(struct esp *esp)
return ent;
}
- if (!spi_populate_tag_msg(&ent->tag[0], cmd)) {
+ if (esp_no_tcq > 0 || !spi_populate_tag_msg(&ent->tag[0], cmd))
{
ent->tag[0] = 0;
ent->tag[1] = 0;
}
@@ -2476,7 +2478,7 @@ static int esp_slave_configure(struct scsi_device *dev)
struct esp *esp = shost_priv(dev->host);
struct esp_target_data *tp = &esp->target[dev->id];
- if (dev->tagged_supported)
+ if (esp_no_tcq <= 0 && dev->tagged_supported)
scsi_change_queue_depth(dev, esp->num_tags);
tp->flags |= ESP_TGT_DISCONNECT;
@@ -2768,6 +2770,9 @@ MODULE_AUTHOR("David S. Miller ([email protected])");
MODULE_LICENSE("GPL");
MODULE_VERSION(DRV_VERSION);
+module_param(esp_no_tcq, int, 0);
+MODULE_PARM_DESC(esp_no_tcq, "Send no command tags");
+
module_param(esp_bus_reset_settle, int, 0);
MODULE_PARM_DESC(esp_bus_reset_settle,
"ESP scsi bus reset delay in seconds");
--
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