[PATCH] 2.6.34-rc3 Disable R_OK (Early ACK) on SII 3726/4726 PMP

[Grant Grundler <grundler@google.com>]

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In 2009, While running "cache read" performance test of drives behind
SII PMP we encountered a "all 5 drives" timeout on more than 30% of the
machines under test.  This patch reduces the rate by a factor of about 70.
Low enough that we didn't care to further investigate the issue.

Performance impact with any sort of "normal" use was ~2%+ CPU and less
than 1% throughput degradation.  Worst case impact (cached read) was
6% IOPS reduction. This is with NCQ off (q=1) but I believe FIS based
switching enabled in the SATA driver.

The patch disables "Early ACK" in the 3726/4726 port multiplier.
"Early ACK" is issued when device sends a FIS to the host (via PMP)
and the PMP sends an ACK immediately back to the device - well before
the host gets the response. Under worst case IOPs load (cached read
test) and more than 2 PMPs connected to a 4-port SATA controller,
I suspect the time to service all of the PMPs is exceeding the PMPs
ability to keep track of outstanding FIS it owes the Host. Reducing
the number of PMPs to 2 (or 1) reduces the frequency by several orders
of magnitude. Kudos to Gwendal for initial debugging of this issue.
[Any errors in the description are mine, not his.]

Patch is currently in production on Google servers.

Signed-off-by: Grant Grundler <grundler@google.com>
Signed-off-by: Gwendal Grignou <gwendal@google.com>

---
And my apologies in advance for using gmail. Patch appended below
is also attached since I expect gmail will mangle the inlined content.

diff --git a/drivers/ata/libata-pmp.c b/drivers/ata/libata-pmp.c
index 00305f4..69bb203 100644
--- a/drivers/ata/libata-pmp.c
+++ b/drivers/ata/libata-pmp.c
@@ -235,6 +235,8 @@ static int sata_pmp_configure(struct ata_device
*dev, int print_info)
 {
        struct ata_port *ap = dev->link->ap;
        u32 *gscr = dev->gscr;
+       u16 vendor = sata_pmp_gscr_vendor(gscr);
+       u16 devid = sata_pmp_gscr_devid(gscr);
        unsigned int err_mask = 0;
        const char *reason;
        int nr_ports, rc;
@@ -260,12 +262,28 @@ static int sata_pmp_configure(struct ata_device
*dev, int print_info)
                goto fail;
        }

+       /* For Sil3726, disable sending Early R_OK */
+       if (vendor == 0x1095 && devid == 0x3726) {
+               u32 reg;
+               err_mask = sata_pmp_read(&ap->link,
SATA_PMP_GSCR_SII_POL, &reg);
+               if (err_mask) {
+                       rc = -EIO;
+                       reason = "failed to read Sil3726 Private Register";
+                       goto fail;
+               }
+               reg &= ~0x1;
+               err_mask = sata_pmp_write(&ap->link,
SATA_PMP_GSCR_SII_POL, reg);
+               if (err_mask) {
+                       rc = -EIO;
+                       reason = "failed to write Sil3726 Private Register";
+                       goto fail;
+               }
+       }
+
        if (print_info) {
                ata_dev_printk(dev, KERN_INFO, "Port Multiplier %s, "
                               "0x%04x:0x%04x r%d, %d ports, feat 0x%x/0x%x\n",
-                              sata_pmp_spec_rev_str(gscr),
-                              sata_pmp_gscr_vendor(gscr),
-                              sata_pmp_gscr_devid(gscr),
+                              sata_pmp_spec_rev_str(gscr), vendor, devid,
                               sata_pmp_gscr_rev(gscr),
                               nr_ports, gscr[SATA_PMP_GSCR_FEAT_EN],
                               gscr[SATA_PMP_GSCR_FEAT]);
diff --git a/include/linux/ata.h b/include/linux/ata.h
index 700c5b9..18fc208 100644
--- a/include/linux/ata.h
+++ b/include/linux/ata.h
@@ -386,6 +386,7 @@ enum {
        SATA_PMP_GSCR_ERROR_EN  = 33,
        SATA_PMP_GSCR_FEAT      = 64,
        SATA_PMP_GSCR_FEAT_EN   = 96,
+       SATA_PMP_GSCR_SII_POL   = 129,  /* VENDOR : Silicon Image 3726/4726 */

        SATA_PMP_PSCR_STATUS    = 0,
        SATA_PMP_PSCR_ERROR     = 1,

[-- Attachment #2: 2.6.18-mv_sata-measure_port_handler-03 --]
[-- Type: application/octet-stream, Size: 4937 bytes --]

==== //depot/google_vendor_src_branch/prodkernel/2.6.18/drivers/scsi/mv_sata/mvIALCommonUtils.c#6 - /usr/local/google/ggg-2.6.18/2.6.18/drivers/scsi/mv_sata/mvIALCommonUtils.c ====
--- /tmp/g4-24719/cache/depot/google_vendor_src_branch/prodkernel/2.6.18/drivers/scsi/mv_sata/mvIALCommonUtils.c#6	2009-07-10 12:08:45.000000000 -0700
+++ /usr/local/google/ggg-2.6.18/2.6.18/drivers/scsi/mv_sata/mvIALCommonUtils.c	2009-07-10 12:08:34.000000000 -0700
@@ -966,6 +966,7 @@ MV_BOOLEAN  mvGetPMDeviceInfo(MV_SATA_AD
     if (pPMDeviceInfo->vendorId == 0x1095 &&
 	(pPMDeviceInfo->deviceId == 0x3726 ||
 	 pPMDeviceInfo->deviceId == 0x4726)) {
+#if 0
       /*
        * Bug 1411341: "CommandAbort in mv_sata during PHY stress test"
        * Clear "Immediate ACK enable" bit so frame ACKs are returned
@@ -977,6 +978,7 @@ MV_BOOLEAN  mvGetPMDeviceInfo(MV_SATA_AD
       regVal &= ~MV_BIT0;
       mvPMDevWriteReg(pSataAdapter, channelIndex, MV_SATA_PM_CONTROL_PORT,
                       129, regVal, NULL);
+#endif
 
       regVal = 5;
       pm_gpio_reg = PM_GSCR_SIL_GPIO;
==== //depot/google_vendor_src_branch/prodkernel/2.6.18/drivers/scsi/mv_sata/mvSata.c#19 - /usr/local/google/ggg-2.6.18/2.6.18/drivers/scsi/mv_sata/mvSata.c ====
--- /tmp/g4-24719/cache/depot/google_vendor_src_branch/prodkernel/2.6.18/drivers/scsi/mv_sata/mvSata.c#19	2009-07-10 10:25:34.000000000 -0700
+++ /usr/local/google/ggg-2.6.18/2.6.18/drivers/scsi/mv_sata/mvSata.c	2009-07-16 22:12:57.000000000 -0700
@@ -7779,6 +7779,11 @@ MV_BOOLEAN mvSataCheckPendingInterrupt(M
     /*bogus interrupt*/
     return MV_FALSE;
 }
+
+#if 1
+#define CPU_MHZ 2200	/* Argo-Barcelona */
+#endif
+
 /*******************************************************************************
 * mvSataInterruptServiceRoutine - Interrupt service routine
 *
@@ -7800,7 +7805,11 @@ MV_BOOLEAN mvSataInterruptServiceRoutine
 {
     MV_U8  sataUnit;
     MV_BUS_ADDR_T ioBaseAddr = pAdapter->adapterIoBaseAddress;
-
+#if 1
+    cycles_t mv_gap, mv_stamp[5];
+    static cycles_t mv_max[5];
+    unsigned char mv_func[5];
+#endif
     mvOsSemTake(&pAdapter->semaphore);
 
     /* Prevent any new interrupts until we are done processing current one.
@@ -7817,7 +7826,17 @@ MV_BOOLEAN mvSataInterruptServiceRoutine
 			MV_SATA_II_ALL_PORTS_INT_CAUSE_REG_OFFSET, 0);
     }
 
+#if 1
+mv_stamp[0] = get_cycles_sync();
+mv_func[0] = 0;
+mv_func[1] = 0;
+mv_func[2] = 0;
+mv_func[3] = 0;
+mv_func[4] = 0;
+sataUnit = 0;
+#else
     for (sataUnit = 0; sataUnit < pAdapter->numberOfUnits; sataUnit++)
+#endif
     {
 	MV_U32 unitCause;
 	MV_U32 unitMask = pAdapter->mainMask;
@@ -7838,7 +7857,7 @@ MV_BOOLEAN mvSataInterruptServiceRoutine
 	 * (This also flushes the previous MMIO write.) */
 	unitCause = MV_REG_READ_DWORD(ioBaseAddr, unitCauseAddr);
 
-	/* derive SATAHC0 Intr Cause mask from mainMask.
+	/* Derive SATAHC0 Intr Cause mask from mainMask.
 	 * typical value of mainMask is 0x0006ab55 .
 	 * FIXME - move this out of line to same places mainMask is set.
 	 */
@@ -7885,6 +7904,9 @@ MV_BOOLEAN mvSataInterruptServiceRoutine
 		MV_U32 ATA_intr = (unitCause >> 8) & portMask;
 
                 if (responseDone) {
+#if 1
+		    mv_func[port] |= 0x10;
+#endif
                     handleEdmaInterrupt(pAdapter, sataUnit, port,
                                         (MV_U8)(unitRspInPtr),
                                         responseDone);
@@ -7901,14 +7923,52 @@ MV_BOOLEAN mvSataInterruptServiceRoutine
 
 			if (mainCause & (1<<(port * 2))) {
 				handleEdmaError(pAdapter, MV_CHANNEL_INDEX(sataUnit, port));
+#if 1
+				mv_func[port] |= 0x2;
+#endif
 			} else {
 				handleDeviceInterrupt(pAdapter, sataUnit, port);
+#if 1
+				mv_func[port] |= 0x4;
+#endif
 			}
                 }
 
                 unitRspInPtr >>= 8;
+
+#if 1
+/* port+1 == end time. port == start time. */
+mv_stamp[port+1] = get_cycles_sync();
+#endif
+            }
+
+#if 1
+/* Defer printing stuff until we've handled everything. */
+for (port = 0; port < pAdapter->portsPerUnit; port++)
+   {
+	cycles_t mv_gap = mv_stamp[port+1]-mv_stamp[port];
+	if ( mv_gap > mv_max[port]) {
+		mv_max[port] = mv_gap;
+		printk(KERN_ERR "mv_sata: SATA%d.%d %llu microsec (0x%llx cycles) 0x%x\n",
+			get_sata_devicenum(pAdapter), port, mv_gap/CPU_MHZ,
+			mv_gap, mv_func[port]);
             }
         }
+
+/* Aggregate time : end time of last port - start time of first port */
+mv_gap = mv_stamp[port] - mv_stamp[0];
+if ( mv_gap > mv_max[port]) {
+	mv_max[port] = mv_gap;
+	printk(KERN_ERR "mv_sata: SATA%d %llu microsec (0x%llx cycles)"
+		" 0x%x 0x%x 0x%x 0x%x\n",
+		get_sata_devicenum(pAdapter),
+		mv_gap/CPU_MHZ, mv_gap,
+		mv_func[0], mv_func[1], mv_func[2], mv_func[3]
+		);
+}
+#endif
+
+        }
         else
         {
 	    MV_U32  edmaError;
@@ -7976,6 +8036,7 @@ MV_BOOLEAN mvSataInterruptServiceRoutine
 	    }
 #endif
         }
+
     }
 
     /* restore MAIN Interrupt Cause Mask register */