On Sun, Nov 03, 2024 at 05:24:09AM +0000, Joe Damato wrote:
> +It is important to note that choosing a large value for ``gro_flush_timeout``
> +will defer IRQs to allow for better batch processing, but will induce latency
> +when the system is not fully loaded. Choosing a small value for
> +``gro_flush_timeout`` can cause interference of the user application which is
> +attempting to busy poll by device IRQs and softirq processing. This value
> +should be chosen carefully with these tradeoffs in mind. epoll-based busy
> +polling applications may be able to mitigate how much user processing happens
> +by choosing an appropriate value for ``maxevents``.
> +
> +Users may want to consider an alternate approach, IRQ suspension, to help deal
to help dealing
> +with these tradeoffs.
> +
> <snipped>...
> +There are essentially three possible loops for network processing and
> +packet delivery:
> +
> +1) hardirq -> softirq -> napi poll; basic interrupt delivery
> +
> +2) timer -> softirq -> napi poll; deferred irq processing
> +
> +3) epoll -> busy-poll -> napi poll; busy looping
The loops list are parsed inconsistently due to tabs between the
enumerators and list items. I have to expand them into single space
(along with number reference fix to follow the output):
---- >8 ----
diff --git a/Documentation/networking/napi.rst b/Documentation/networking/napi.rst
index bbd58bcc430fab..848cb19f0becc1 100644
--- a/Documentation/networking/napi.rst
+++ b/Documentation/networking/napi.rst
@@ -375,23 +375,21 @@ epoll finds no events, the setting of ``gro_flush_timeout`` and
There are essentially three possible loops for network processing and
packet delivery:
-1) hardirq -> softirq -> napi poll; basic interrupt delivery
+1) hardirq -> softirq -> napi poll; basic interrupt delivery
+2) timer -> softirq -> napi poll; deferred irq processing
+3) epoll -> busy-poll -> napi poll; busy looping
-2) timer -> softirq -> napi poll; deferred irq processing
-
-3) epoll -> busy-poll -> napi poll; busy looping
-
-Loop 2) can take control from Loop 1), if ``gro_flush_timeout`` and
+Loop 2 can take control from Loop 1, if ``gro_flush_timeout`` and
``napi_defer_hard_irqs`` are set.
-If ``gro_flush_timeout`` and ``napi_defer_hard_irqs`` are set, Loops 2)
-and 3) "wrestle" with each other for control.
+If ``gro_flush_timeout`` and ``napi_defer_hard_irqs`` are set, Loops 2
+and 3 "wrestle" with each other for control.
-During busy periods, ``irq-suspend-timeout`` is used as timer in Loop 2),
-which essentially tilts network processing in favour of Loop 3).
+During busy periods, ``irq-suspend-timeout`` is used as timer in Loop 2,
+which essentially tilts network processing in favour of Loop 3.
-If ``gro_flush_timeout`` and ``napi_defer_hard_irqs`` are not set, Loop 3)
-cannot take control from Loop 1).
+If ``gro_flush_timeout`` and ``napi_defer_hard_irqs`` are not set, Loop 3
+cannot take control from Loop 1.
Therefore, setting ``gro_flush_timeout`` and ``napi_defer_hard_irqs`` is
the recommended usage, because otherwise setting ``irq-suspend-timeout``
Thanks.
--
An old man doll... just what I always wanted! - Clara
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