Re: [RFC net-next 4/5] eventpoll: Trigger napi_busy_loop, if prefer_busy_poll is set

[Matthew Wilcox]

On Mon, Aug 12, 2024 at 06:19:35AM -0700, Christoph Hellwig wrote:
> On Mon, Aug 12, 2024 at 12:57:07PM +0000, Joe Damato wrote:
> > From: Martin Karsten <mkarsten@xxxxxxxxxxxx>
> > 
> > Setting prefer_busy_poll now leads to an effectively nonblocking
> > iteration though napi_busy_loop, even when busy_poll_usecs is 0.
> 
> Hardcoding calls to the networking code from VFS code seems like
> a bad idea.   Not that I disagree with the concept of disabling
> interrupts during busy polling, but this needs a proper abstraction
> through file_operations.

I don't understand what's going on with this patch set.  Is it just
working around badly designed hardware?  NVMe is specified in a way that
lets it be completely interruptless if the host is keeping up with the
incoming completions from the device (ie the device will interrupt if a
completion has been posted for N microseconds without being acknowledged).
I assumed this was how network devices worked too, but I didn't check.