[dpdk-dev] [PATCH v3] net/mlx4: fix dev rmv not detected after port stop

Adrien Mazarguil adrien.mazarguil at 6wind.com
Wed Jan 31 10:15:13 CET 2018


On Tue, Jan 30, 2018 at 08:37:06PM +0000, Shahaf Shuler wrote:
> Tuesday, January 30, 2018 11:40 AM, Adrien Mazarguil:
> > Unfortunately I didn't get a chance to review this patch before it was applied.
> > I'm not sure a stopped port is supposed to report events (interrupts). Will
> > applications expect them to occur at this point?
> 
> Why not?
> 
> Stopped port is still counted as attached. The fact the application stopped the packet receive on it doesn't mean it should not receive a sync events (such as the remove event).
> async events, by definition, are not related to traffic being flows through the port. 

My comment is based on my understanding of rte_eth_dev_stop(), which is a
device (or port) is completely stopped, in a suspended state and no
interrupts shall occur, as a means for applications to temporarily not be
bothered by them until restarted.

Think about it that way: applications do not want to get interrupts
immediately after the device is initialized, because they might not be ready
to process them at this point. An explicit call to rte_eth_dev_start() tells
the PMD when it's OK to do so. The converse is rte_eth_dev_stop().

Stopping traffic can already be achieved by not polling from the application
side, calling rte_eth_dev_[rt]x_queue_stop() and/or toggling RX/TX
interrupts through rte_eth_dev_[rt]x_intr_enable(). rte_eth_dev_stop()
provides lower-level device control.

Perhaps documentation is not clear, however that's how LSC seems implemented
in all PMDs; it gets disabled after rte_eth_dev_stop() and one should
explicitly use rte_eth_link_get() to retrieve link status afterward. I think
RMV should behave similarly with rte_eth_dev_is_removed(). Adapting
fail-safe should be easier than modifying all the remaining PMDs.

> > In my opinion it's not a fix, as in, it doesn't address an issue introduced by the
> > mentioned patch whose behavior was correct.
> > 
> > It's probably too late to change it now and it does address an issue seen with
> > a use case involving this PMD, however I think the fail-safe PMD could as well
> > poll using the recently-added rte_eth_dev_is_removed() when it's aware
> > the underlying port is stopped instead of expecting interrupts.
> > 
> > --
> > Adrien Mazarguil
> > 6WIND

-- 
Adrien Mazarguil
6WIND


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