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pci: Optimise MSI-X table programming

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With an updated Linux kernel the kernel reprograms the same table entry
in the MSI-X table multiple times. Fortunately it does so with entry
masked (the default.)

The costly part of MSI-X table reprogramming is going out to the host
kernel to update the GSI routing entries. This change makes three
optimisations.

1. If the table entry is unchanged: skip handking updates
2. Only update the GSI routing table if the table entry is unmasked
   (this skips extra calls to the ioctl() for reprogramming the
    entries.)
3. Only generate a message on entry unmasking if the global MSI-X enable
   bit is set.

Fixes: #4273

Signed-off-by: Rob Bradford <robert.bradford@intel.com>
This commit is contained in:
Rob Bradford 2022-10-07 15:34:10 +01:00 committed by Bo Chen
parent 29cf637f3f
commit 89a2562c5a
1 changed files with 22 additions and 16 deletions
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38
pci/src/msix.rs
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@ -35,7 +35,7 @@ enum Error {
UpdateInterruptRoute(io::Error),
}
#[derive(Debug, Clone, Versionize)]
#[derive(Debug, Clone, Versionize, Eq, PartialEq)]
pub struct MsixTableEntry {
pub msg_addr_lo: u32,
pub msg_addr_hi: u32,
@ -258,7 +258,7 @@ impl MsixConfig {
let modulo_offset = offset % MSIX_TABLE_ENTRIES_MODULO;
// Store the value of the entry before modification
let mut old_entry: Option<MsixTableEntry> = None;
let old_entry = self.table_entries[index].clone();
match data.len() {
4 => {
@ -268,7 +268,6 @@ impl MsixConfig {
0x4 => self.table_entries[index].msg_addr_hi = value,
0x8 => self.table_entries[index].msg_data = value,
0xc => {
old_entry = Some(self.table_entries[index].clone());
self.table_entries[index].vector_ctl = value;
}
_ => error!("invalid offset"),
@ -284,7 +283,6 @@ impl MsixConfig {
self.table_entries[index].msg_addr_hi = (value >> 32) as u32;
}
0x8 => {
old_entry = Some(self.table_entries[index].clone());
self.table_entries[index].msg_data = (value & 0xffff_ffffu64) as u32;
self.table_entries[index].vector_ctl = (value >> 32) as u32;
}
@ -296,10 +294,18 @@ impl MsixConfig {
_ => error!("invalid data length"),
};
// Update interrupt routes
if self.enabled && !self.masked {
let table_entry = &self.table_entries[index];
let table_entry = &self.table_entries[index];
// Optimisation to avoid excessive updates
if &old_entry == table_entry {
return;
}
// Update interrupt routes
// Optimisation: only update routes if the entry is not masked;
// this is safe because if the entry is masked (starts masked as per spec)
// in the table then it won't be triggered. (See: #4273)
if self.enabled && !self.masked && !table_entry.masked() {
let config = MsiIrqSourceConfig {
high_addr: table_entry.msg_addr_hi,
low_addr: table_entry.msg_addr_lo,
@ -323,15 +329,15 @@ impl MsixConfig {
// has been injected, the pending bit in the PBA needs to be cleared.
// All of this is valid only if MSI-X has not been masked for the whole
// device.
if let Some(old_entry) = old_entry {
// Check if bit has been flipped
if !self.masked()
&& old_entry.masked()
&& !self.table_entries[index].masked()
&& self.get_pba_bit(index as u16) == 1
{
self.inject_msix_and_clear_pba(index);
}
// Check if bit has been flipped
if !self.masked()
&& self.enabled()
&& old_entry.masked()
&& !table_entry.masked()
&& self.get_pba_bit(index as u16) == 1
{
self.inject_msix_and_clear_pba(index);
}
}