From b6ba0f9fad93f7062098420602d407f9baeec775 Mon Sep 17 00:00:00 2001
From: drblah <theblahblah2001@gmail.com>
Date: Fri, 31 Dec 2021 12:56:15 +0100
Subject: [PATCH] Kernel: Update E1000 link state using interrupt

Calls to link_up() in the E1000 driver would read the link state
directly from the hardware on every call. This had negative
performance impact in high throughput situations since link_up()
is called every time an IP packet's route is resolved.

This patch takes inspiration from the RTL8139 network adapter where
the link state is stored in a bool and only updated when the hardware
generates an interrupt related to link state change.

After this change I measured a ~9% increase in TCP Tx throughput
using:
cat /dev/zero | nc <host_IP> <host_port> from the Serenity VM to my
host machine
---
 Kernel/Net/Intel/E1000NetworkAdapter.cpp | 10 +++++-----
 Kernel/Net/Intel/E1000NetworkAdapter.h   |  3 ++-
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/Kernel/Net/Intel/E1000NetworkAdapter.cpp b/Kernel/Net/Intel/E1000NetworkAdapter.cpp
index 0f6240c5fb..8d3db08ae8 100644
--- a/Kernel/Net/Intel/E1000NetworkAdapter.cpp
+++ b/Kernel/Net/Intel/E1000NetworkAdapter.cpp
@@ -221,6 +221,9 @@ UNMAP_AFTER_INIT bool E1000NetworkAdapter::initialize()
 
     setup_link();
     setup_interrupts();
+
+    m_link_up = ((in32(REG_STATUS) & STATUS_LU) != 0);
+
     return true;
 }
 
@@ -249,6 +252,8 @@ bool E1000NetworkAdapter::handle_irq(const RegisterState&)
     if (status & INTERRUPT_LSC) {
         u32 flags = in32(REG_CTRL);
         out32(REG_CTRL, flags | ECTRL_SLU);
+
+        m_link_up = ((in32(REG_STATUS) & STATUS_LU) != 0);
     }
     if (status & INTERRUPT_RXDMT0) {
         // Threshold OK?
@@ -315,11 +320,6 @@ UNMAP_AFTER_INIT void E1000NetworkAdapter::read_mac_address()
     }
 }
 
-bool E1000NetworkAdapter::link_up()
-{
-    return (in32(REG_STATUS) & STATUS_LU);
-}
-
 UNMAP_AFTER_INIT void E1000NetworkAdapter::initialize_rx_descriptors()
 {
     auto* rx_descriptors = (e1000_tx_desc*)m_rx_descriptors_region->vaddr().as_ptr();
diff --git a/Kernel/Net/Intel/E1000NetworkAdapter.h b/Kernel/Net/Intel/E1000NetworkAdapter.h
index 8ed931c563..0ce4806b6c 100644
--- a/Kernel/Net/Intel/E1000NetworkAdapter.h
+++ b/Kernel/Net/Intel/E1000NetworkAdapter.h
@@ -27,7 +27,7 @@ public:
     virtual ~E1000NetworkAdapter() override;
 
     virtual void send_raw(ReadonlyBytes) override;
-    virtual bool link_up() override;
+    virtual bool link_up() override { return m_link_up; };
     virtual i32 link_speed() override;
     virtual bool link_full_duplex() override;
 
@@ -93,6 +93,7 @@ protected:
     OwnPtr<Memory::Region> m_mmio_region;
     bool m_has_eeprom { false };
     bool m_use_mmio { false };
+    bool m_link_up { false };
     EntropySource m_entropy_source;
 
     WaitQueue m_wait_queue;