On 2/4/21 2:06 PM, Marcelo Tosatti wrote:

On Thu, Feb 04, 2021 at 01:47:38PM -0500, Nitesh Narayan Lal wrote:

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Nitesh, is there anything preventing this from being fixed
in userspace ? (as Thomas suggested previously).

Everything with is not managed can be steered by user space.

Yes, but it seems to be racy (that is, there is a window where the 
interrupt can be delivered to an isolated CPU).

ethtool ->
xgbe_set_channels ->
xgbe_full_restart_dev ->
xgbe_alloc_memory ->
xgbe_alloc_channels ->
cpumask_local_spread

Also ifconfig eth0 down / ifconfig eth0 up leads
to cpumask_spread_local.

There's always that possibility.

Then there is a window where isolation can be broken.

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We have to ensure that we move the IRQs by a tuned daemon or some other
userspace script every time there is a net-dev change (eg. device comes up,
creates VFs, etc).

Again, race window open can result in interrupt to isolated CPU.

Yes, and if I am not mistaken then that always has been a problem with
these userspace solutions.

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How about adding a new flag for isolcpus instead?

Do you mean a flag based on which we can switch the affinity mask to
housekeeping for all the devices at the time of IRQ distribution?

Yes a new flag for isolcpus. HK_FLAG_IRQ_SPREAD or some better name.

Does sounds like a nice idea to explore, lets see what Thomas thinks about it.

-- 
Thanks
Nitesh