svn commit: r360985 - stable/12/sys/dev/ena

[Marcin Wojtas]

wt., 12 maj 2020 o 20:44 Marcin Wojtas <mw at freebsd.org> napisał(a):
>
> Author: mw
> Date: Tue May 12 18:44:41 2020
> New Revision: 360985
> URL: https://svnweb.freebsd.org/changeset/base/360985
>
> Log:
>   MFC r360777: Optimize ENA Rx refill for low memory conditions
>
>   Sometimes, especially when there is not much memory in the system left,
>   allocating mbuf jumbo clusters (like 9KB or 16KB) can take a lot of time
>   and it is not guaranteed that it'll succeed. In that situation, the
>   fallback will work, but if the refill needs to take a place for a lot of
>   descriptors at once, the time spent in m_getjcl looking for memory can
>   cause system unresponsiveness due to high priority of the Rx task. This
>   can also lead to driver reset, because Tx cleanup routine is being
>   blocked and timer service could detect that Tx packets aren't cleaned
>   up. The reset routine can further create another unresponsiveness - Rx
>   rings are being refilled there, so m_getjcl will again burn the CPU.
>   This was causing NVMe driver timeouts and resets, because network driver
>   is having higher priority.
>
>   Instead of 16KB jumbo clusters for the Rx buffers, 9KB clusters are
>   enough - ENA MTU is being set to 9K anyway, so it's very unlikely that
>   more space than 9KB will be needed.
>
>   However, 9KB jumbo clusters can still cause issues, so by default the
>   page size mbuf cluster will be used for the Rx descriptors. This can have a
>   small (~2%) impact on the throughput of the device, so to restore
>   original behavior, one must change sysctl "hw.ena.enable_9k_mbufs" to
>   "1" in "/boot/loader.conf" file.
>
>   As a part of this patch (important fix), the version of the driver
>   was updated to v2.1.2.
>

For the record - on stable/12 the version was bumped to 0.8.5 with this commit.

Marcin