mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-05-03 20:34:23 -04:00
e13b6da704
There are several issues existed in start_xmit(): - Transmitted packets need to be freed before sending a packet, this introduces delay and increases the average packets transmit time. This also increase the time that spent in holding the TX lock. - Notification is enabled after free_old_xmit_skbs() which will introduce unnecessary interrupts if TX notification happens on the same CPU that is doing the transmission now (actually, virtio-net driver are optimized for this case). So this patch tries to avoid those issues by not cleaning transmitted packets in start_xmit() when TX NAPI is enabled and disable notifications even more aggressively. Notification will be since the beginning of the start_xmit(). But we can't enable delayed notification after TX is stopped as we will lose the notifications. Instead, the delayed notification needs is enabled after the virtqueue is kicked for best performance. Performance numbers: 1) single queue 2 vcpus guest with pktgen_sample03_burst_single_flow.sh (burst 256) + testpmd (rxonly) on the host: - When pinning TX IRQ to pktgen VCPU: split virtqueue PPS were increased 55% from 6.89 Mpps to 10.7 Mpps and 32% TX interrupts were eliminated. Packed virtqueue PPS were increased 50% from 7.09 Mpps to 10.7 Mpps, 99% TX interrupts were eliminated. - When pinning TX IRQ to VCPU other than pktgen: split virtqueue PPS were increased 96% from 5.29 Mpps to 10.4 Mpps and 45% TX interrupts were eliminated; Packed virtqueue PPS were increased 78% from 6.12 Mpps to 10.9 Mpps and 99% TX interrupts were eliminated. 2) single queue 1 vcpu guest + vhost-net/TAP on the host: single session netperf from guest to host shows 82% improvement from 31Gb/s to 58Gb/s, %stddev were reduced from 34.5% to 1.9% and 88% of TX interrupts were eliminated. Signed-off-by: Jason Wang <jasowang@redhat.com> Acked-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.