linux-kernel - [PATCH net-next v3 0/2] vsock: avoid queuing on workqueue if possible

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Message-Id: <20240711-pinna-v3-0-697d4164fe80@outlook.com>
Date: Thu, 11 Jul 2024 16:58:45 +0200
From: Luigi Leonardi via B4 Relay <devnull+luigi.leonardi.outlook.com@...nel.org>
To: Stefan Hajnoczi <stefanha@...hat.com>, 
 Stefano Garzarella <sgarzare@...hat.com>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: kvm@...r.kernel.org, virtualization@...ts.linux.dev, 
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Luigi Leonardi <luigi.leonardi@...look.com>, 
 Marco Pinna <marco.pinn95@...il.com>
Subject: [PATCH net-next v3 0/2] vsock: avoid queuing on workqueue if
 possible

This series introduces an optimization for vsock/virtio to reduce latency
and increase the throughput: When the guest sends a packet to the host, 
and the workqueue is empty, if there is enough space, the packet is put
directly in the virtqueue.

v2->v3
- Performed more experiments using iperf3 using multiple streams
- Handling of reply packets removed from virtio_transport_send_skb,
  as is needed just by the worker. 
- Removed atomic_inc/atomic_sub when queuing directly to the vq.
- Introduced virtio_transport_send_skb_fast_path that handles the
  steps for sending on the vq. 
- Fixed a missing mutex_unlock in error path.
- Changed authorship of the second commit
- Rebased on latest net-next

v1->v2
In this v2 I replaced a mutex_lock with a mutex_trylock because it was
insidea RCU critical section. I also added a check on tx_run, so if the
module is being removed the packet is not queued. I'd like to thank Stefano
for reporting the tx_run issue.

Applied all Stefano's suggestions:
    - Minor code style changes
    - Minor commit text rewrite
Performed more experiments:
     - Check if all the packets go directly to the vq (Matias' suggestion)
     - Used iperf3 to see if there is any improvement in overall throughput
      from guest to host
     - Pinned the vhost process to a pCPU.
     - Run fio using 512B payload
Rebased on latest net-next

To: Stefan Hajnoczi <stefanha@...hat.com>
To: Stefano Garzarella <sgarzare@...hat.com>
To: David S. Miller <davem@...emloft.net>
To: Eric Dumazet <edumazet@...gle.com>
To: Jakub Kicinski <kuba@...nel.org>
To: Paolo Abeni <pabeni@...hat.com>
Cc: kvm@...r.kernel.org
Cc: virtualization@...ts.linux.dev
Cc: netdev@...r.kernel.org
Cc: linux-kernel@...r.kernel.org

Signed-off-by: Luigi Leonardi <luigi.leonardi@...look.com>
---
Luigi Leonardi (1):
      vsock/virtio: avoid queuing packets when work queue is empty

Marco Pinna (1):
      vsock/virtio: refactor virtio_transport_send_pkt_work

 net/vmw_vsock/virtio_transport.c | 143 +++++++++++++++++++++++++--------------
 1 file changed, 93 insertions(+), 50 deletions(-)
---
base-commit: 58f9416d413aa2c20b2515233ce450a1607ef843
change-id: 20240711-pinna-49bf0ab09909

Best regards,
-- 
Luigi Leonardi <luigi.leonardi@...look.com>