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

[Joe Damato]

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.

Thanks for the feedback; the code modified in the this patch was
already calling directly into the networking stack; we didn't add
that call. We added a check on another member of the eventpoll
structure, though.

In general: it may be appropriate for a better abstraction to exist
between fs/eventpoll.c and the networking stack as there are already
many calls into the networking stack from this code.

However, I think that is a much larger change that is not directly
related to what we're proposing, which is: a mechanism for more
efficient epoll-based busy poll which shows significant performance
improvements.

- Joe