From db96605a49b334eeb2a5d1cc12981778f7d792aa Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alex=20Benn=C3=A9e?= <alex.bennee@linaro.org>
Date: Mon, 24 Oct 2022 11:20:15 +0200
Subject: [PATCH] ssi: cache SSIPeripheralClass to avoid GET_CLASS()
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Investigating why some BMC models are so slow compared to a plain ARM
virt machines I did some profiling of:

  ./qemu-system-arm -M romulus-bmc -nic user \
    -drive
    file=obmc-phosphor-image-romulus.static.mtd,format=raw,if=mtd \
    -nographic -serial mon:stdio

And saw that object_class_dynamic_cast_assert was dominating the
profile times. We have a number of cases in this model of the SSI bus.
As the class is static once the object is created we just cache it and
use it instead of the dynamic case macros.

Profiling against:

  ./tests/venv/bin/avocado run \
    tests/avocado/machine_aspeed.py:test_arm_ast2500_romulus_openbmc_v2_9_0

Before: 35.565 s ±  0.087 s
After: 15.713 s ±  0.287 s

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Cc: Cédric Le Goater <clg@kaod.org>
Tested-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20220811151413.3350684-6-alex.bennee@linaro.org>
Message-Id: <20220923084803.498337-6-clg@kaod.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
---
 hw/ssi/ssi.c         | 18 ++++++++----------
 include/hw/ssi/ssi.h |  3 +++
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/hw/ssi/ssi.c b/hw/ssi/ssi.c
index 003931fb50..d54a109bee 100644
--- a/hw/ssi/ssi.c
+++ b/hw/ssi/ssi.c
@@ -38,9 +38,8 @@ static void ssi_cs_default(void *opaque, int n, int level)
     bool cs = !!level;
     assert(n == 0);
     if (s->cs != cs) {
-        SSIPeripheralClass *ssc = SSI_PERIPHERAL_GET_CLASS(s);
-        if (ssc->set_cs) {
-            ssc->set_cs(s, cs);
+        if (s->spc->set_cs) {
+            s->spc->set_cs(s, cs);
         }
     }
     s->cs = cs;
@@ -48,11 +47,11 @@ static void ssi_cs_default(void *opaque, int n, int level)
 
 static uint32_t ssi_transfer_raw_default(SSIPeripheral *dev, uint32_t val)
 {
-    SSIPeripheralClass *ssc = SSI_PERIPHERAL_GET_CLASS(dev);
+    SSIPeripheralClass *ssc = dev->spc;
 
     if ((dev->cs && ssc->cs_polarity == SSI_CS_HIGH) ||
-            (!dev->cs && ssc->cs_polarity == SSI_CS_LOW) ||
-            ssc->cs_polarity == SSI_CS_NONE) {
+        (!dev->cs && ssc->cs_polarity == SSI_CS_LOW) ||
+        ssc->cs_polarity == SSI_CS_NONE) {
         return ssc->transfer(dev, val);
     }
     return 0;
@@ -67,6 +66,7 @@ static void ssi_peripheral_realize(DeviceState *dev, Error **errp)
             ssc->cs_polarity != SSI_CS_NONE) {
         qdev_init_gpio_in_named(dev, ssi_cs_default, SSI_GPIO_CS, 1);
     }
+    s->spc = ssc;
 
     ssc->realize(s, errp);
 }
@@ -115,13 +115,11 @@ uint32_t ssi_transfer(SSIBus *bus, uint32_t val)
 {
     BusState *b = BUS(bus);
     BusChild *kid;
-    SSIPeripheralClass *ssc;
     uint32_t r = 0;
 
     QTAILQ_FOREACH(kid, &b->children, sibling) {
-        SSIPeripheral *peripheral = SSI_PERIPHERAL(kid->child);
-        ssc = SSI_PERIPHERAL_GET_CLASS(peripheral);
-        r |= ssc->transfer_raw(peripheral, val);
+        SSIPeripheral *p = SSI_PERIPHERAL(kid->child);
+        r |= p->spc->transfer_raw(p, val);
     }
 
     return r;
diff --git a/include/hw/ssi/ssi.h b/include/hw/ssi/ssi.h
index f411858ab0..6950f86810 100644
--- a/include/hw/ssi/ssi.h
+++ b/include/hw/ssi/ssi.h
@@ -59,6 +59,9 @@ struct SSIPeripheralClass {
 struct SSIPeripheral {
     DeviceState parent_obj;
 
+    /* cache the class */
+    SSIPeripheralClass *spc;
+
     /* Chip select state */
     bool cs;
 };