Re: [PATCH 0/10] psi: pressure stall information for CPU, memory, and IO v2

[Johannes Weiner]

On Thu, Jul 12, 2018 at 04:44:22PM -0700, Andrew Morton wrote:
> On Thu, 12 Jul 2018 13:29:32 -0400 Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
> 
> >
> > ...
> >
> > The io file is similar to memory. Because the block layer doesn't have
> > a concept of hardware contention right now (how much longer is my IO
> > request taking due to other tasks?), it reports CPU potential lost on
> > all IO delays, not just the potential lost due to competition.
> 
> Probably dumb question: disks aren't the only form of IO.  Does it make
> sense to accumulate PSI for other forms of IO?  Networking comes to
> mind...

It's conceivable, although I haven't thought too much about it yet. If
that turns out to be a state we might want to track, we can easily add
a task state to identify such stalls and add /proc/pressure/net e.g.

"io" in this case means only the block layer / filesystems. I think
keeping this distinction makes sense in the interest of identifying
which type of hardware resource is posing a pressure problem.