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vsock: reduce credit update messages sent to guest

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Earlier we were sending credit update messages to guest
everytime data was read, now we send it only if the available
space is less than 1/4th of the tx buffer size.

benchmarks:

host->guest[Gbps]

before   1.45
after    1.51

guest->host[Gbps]

before   5.68
after    6.07

Note: I did 3 runs of 10 secs and took average of all,
they are relative results.

Fixes #317

Signed-off-by: Ramyak Mehra <rmehra_be19@thapar.edu>

[SG: fixed S-o-b and small things in the commit description]

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
This commit is contained in:
Ramyak Mehra 2023-04-15 01:44:39 +05:30 committed by Viresh Kumar
parent 0b7f536998
commit e24d3e52fc
1 changed files with 17 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
crates/vsock/src/vsock_conn.rs
View File

@ -52,6 +52,8 @@ pub(crate) struct VsockConnection<S> {
pub epoll_fd: RawFd,
/// Local tx buffer.
pub tx_buf: LocalTxBuf,
/// Local tx buffer size
tx_buffer_size: u32,
}
impl<S: AsRawFd + Read + Write> VsockConnection<S> {
@ -81,6 +83,7 @@ impl<S: AsRawFd + Read + Write> VsockConnection<S> {
rx_cnt: Wrapping(0),
epoll_fd,
tx_buf: LocalTxBuf::new(tx_buffer_size),
tx_buffer_size,
}
}
@ -114,6 +117,7 @@ impl<S: AsRawFd + Read + Write> VsockConnection<S> {
rx_cnt: Wrapping(0),
epoll_fd,
tx_buf: LocalTxBuf::new(tx_buffer_size),
tx_buffer_size,
}
}
@ -308,8 +312,18 @@ impl<S: AsRawFd + Read + Write> VsockConnection<S> {
if written_count > 0 {
// Increment forwarded count by number of bytes written to the stream
self.fwd_cnt += Wrapping(written_count as u32);
// TODO: https://github.com/torvalds/linux/commit/c69e6eafff5f725bc29dcb8b52b6782dca8ea8a2
self.rx_queue.enqueue(RxOps::CreditUpdate);
// At what point in available credits should we send a credit update.
// This is set to 1/4th of the tx buffer size. If we keep it too low,
// we will end up sending too many credit updates. If we keep it too
// high, we will end up sending too few credit updates and cause stalls.
// Stalls are more bad than too many credit updates.
let free_space = self
.tx_buffer_size
.wrapping_sub((self.fwd_cnt - self.last_fwd_cnt).0);
if free_space < self.tx_buffer_size / 4 {
self.rx_queue.enqueue(RxOps::CreditUpdate);
}
}
if written_count != buf.len() {
@ -332,7 +346,7 @@ impl<S: AsRawFd + Read + Write> VsockConnection<S> {
.set_src_port(self.local_port)
.set_dst_port(self.peer_port)
.set_type(VSOCK_TYPE_STREAM)
.set_buf_alloc(self.tx_buf.get_buf_size())
.set_buf_alloc(self.tx_buffer_size)
.set_fwd_cnt(self.fwd_cnt.0)
}