[Qemu-devel] [PATCH v4] lsi_scsi: Reselection needed to remove pending commands from queue

[George Kennedy]

Under heavy IO (e.g. fio) the queue is not checked frequently enough for
pending commands. As a result some pending commands are timed out by the
linux sym53c8xx driver, which sends SCSI Abort messages for the timed out
commands. The SCSI Abort messages result in linux errors, which show up
on the console and in /var/log/messages.

e.g.
sd 0:0:3:0: [sdd] tag#33 ABORT operation started
scsi target0:0:3: control msgout:
80 20 47 d
sd 0:0:3:0: ABORT operation complete.
scsi target0:0:4: message d sent on bad reselection

When the current command completes, check if there is a pending command
on the queue and if a pending command exists, set a flag indicating
that a Wait Reselect command is needed to handle a queued pending command.

When a Wait Reselect is needed, intercept and save the current DMA Scripts
Ptr (DSP) contents and load it instead with the pointer to the Reselection
Scripts.  When Reselection has completed, restore the original DSP contents.

Signed-off-by: George Kennedy <address@hidden>
---

Thanks Paolo,

For the question about why the "- 8" in "s->resel_dsp = s->dsp - 8". Notice
that at the beginning of lsi_execute_script() just before the
"switch (insn >> 30)" the "s->dsp += 8". All that's being done with the "- 8"
is to restore the dsp to what it was when "insn" was read. I tried it without
the "- 8" and it fails.

Also, in all my testing the address for the Reselection Scripts never changes.
That's why I only saved it once in "s->resel_dsp". I took out the "if" check
that was done to see if "s->resel_dsp" is already loaded and just reload it
each time lsi_wait_reselect() is called.

The theory that "missing a call to lsi_wait_reselect" is occurring is not
the case. Now everytime "s->resel_dsp = s->dsp - 8" is run a call to
lsi_wait_reselect() occurs as well.

The original patch handling of when "s->next_dsp = s->resel_dsp" should be run
has been restored.

Finally, I need to come up with a FIXME. Does it belong in the commit or in
lsi53c895a.c or both? If the FIXME should be in lsi53c895a.c, where should I
put it?

BTW, in a quick check of fio results read results improve by ~5% (makes
sense as reads were getting penalized by ending up on the pending queue) and
write performance remains the same.


 hw/scsi/lsi53c895a.c | 63 +++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 52 insertions(+), 11 deletions(-)

diff --git a/hw/scsi/lsi53c895a.c b/hw/scsi/lsi53c895a.c
index d1e6534..aff5e27 100644
--- a/hw/scsi/lsi53c895a.c
+++ b/hw/scsi/lsi53c895a.c
@@ -219,6 +219,9 @@ typedef struct {
     int command_complete;
     QTAILQ_HEAD(, lsi_request) queue;
     lsi_request *current;
+    bool want_resel;    /* need resel to handle queued completed cmds */
+    uint32_t resel_dsp; /* DMA Scripts Ptr (DSP) of reselection scsi scripts */
+    uint32_t next_dsp;  /* if want_resel, will be loaded with above */
 
     uint32_t dsa;
     uint32_t temp;
@@ -298,6 +301,18 @@ static inline int lsi_irq_on_rsl(LSIState *s)
     return (s->sien0 & LSI_SIST0_RSL) && (s->scid & LSI_SCID_RRE);
 }
 
+static lsi_request *get_pending_req(LSIState *s)
+{
+    lsi_request *p;
+
+    QTAILQ_FOREACH(p, &s->queue, next) {
+        if (p->pending) {
+            return p;
+        }
+    }
+    return NULL;
+}
+
 static void lsi_soft_reset(LSIState *s)
 {
     trace_lsi_reset();
@@ -446,7 +461,6 @@ static void lsi_update_irq(LSIState *s)
 {
     int level;
     static int last_level;
-    lsi_request *p;
 
     /* It's unclear whether the DIP/SIP bits should be cleared when the
        Interrupt Status Registers are cleared or when istat0 is read.
@@ -477,12 +491,12 @@ static void lsi_update_irq(LSIState *s)
     lsi_set_irq(s, level);
 
     if (!level && lsi_irq_on_rsl(s) && !(s->scntl1 & LSI_SCNTL1_CON)) {
+        lsi_request *p;
+
         trace_lsi_update_irq_disconnected();
-        QTAILQ_FOREACH(p, &s->queue, next) {
-            if (p->pending) {
-                lsi_reselect(s, p);
-                break;
-            }
+        p = get_pending_req(s);
+        if (p) {
+            lsi_reselect(s, p);
         }
     }
 }
@@ -759,6 +773,8 @@ static void lsi_command_complete(SCSIRequest *req, uint32_t 
status, size_t resid
         lsi_request_free(s, s->current);
         scsi_req_unref(req);
     }
+    s->want_resel = get_pending_req(s) ? true : false;
+
     lsi_resume_script(s);
 }
 
@@ -1064,17 +1080,21 @@ static void lsi_wait_reselect(LSIState *s)
 
     trace_lsi_wait_reselect();
 
-    QTAILQ_FOREACH(p, &s->queue, next) {
-        if (p->pending) {
-            lsi_reselect(s, p);
-            break;
-        }
+    if (s->current) {
+        return;
+    }
+
+    p = get_pending_req(s);
+    if (p) {
+        lsi_reselect(s, p);
     }
     if (s->current == NULL) {
         s->waiting = 1;
     }
 }
 
+#define SCRIPTS_LOAD_AND_STORE  0xe2340004
+
 static void lsi_execute_script(LSIState *s)
 {
     PCIDevice *pci_dev = PCI_DEVICE(s);
@@ -1082,10 +1102,15 @@ static void lsi_execute_script(LSIState *s)
     uint32_t addr, addr_high;
     int opcode;
     int insn_processed = 0;
+    uint32_t save_dsp = 0;
 
     s->istat1 |= LSI_ISTAT1_SRUN;
 again:
     insn_processed++;
+    if (s->next_dsp) {
+        save_dsp = s->dsp;
+        s->dsp = s->next_dsp;
+    }
     insn = read_dword(s, s->dsp);
     if (!insn) {
         /* If we receive an empty opcode increment the DSP by 4 bytes
@@ -1093,6 +1118,10 @@ again:
         s->dsp += 4;
         goto again;
     }
+    if (s->want_resel && s->resel_dsp && (insn == SCRIPTS_LOAD_AND_STORE)) {
+        s->next_dsp = s->resel_dsp;
+        s->want_resel = 0;
+     }
     addr = read_dword(s, s->dsp + 4);
     addr_high = 0;
     trace_lsi_execute_script(s->dsp, insn, addr);
@@ -1260,7 +1289,19 @@ again:
                 s->scntl1 &= ~LSI_SCNTL1_CON;
                 break;
             case 2: /* Wait Reselect */
+                if (save_dsp == 0) {
+                    /*
+                     * dsp is advanced by 8 after loading the instruction
+                     * at top of this routine. Adjust dsp back to what it
+                     * was to get start address of Reselect Scripts.
+                     */
+                    s->resel_dsp = s->dsp - 8;
+                }
                 if (!lsi_irq_on_rsl(s)) {
+                    if (save_dsp) {
+                        s->dsp = save_dsp;
+                        save_dsp = s->next_dsp = 0;
+                    }
                     lsi_wait_reselect(s);
                 }
                 break;
-- 
1.8.3.1