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Kernel: Update E1000 link state using interrupt

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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
This commit is contained in:
drblah 2021-12-31 12:56:15 +01:00 • committed by Andreas Kling
parent d7f6635d55
commit b6ba0f9fad
2 changed files with 7 additions and 6 deletions
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10
Kernel/Net/Intel/E1000NetworkAdapter.cpp
View file

@ -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();