2024-02-05 21:58:23

by Joe Damato

Subject: [PATCH net-next v6 3/4] eventpoll: Add per-epoll prefer busy poll option

When using epoll-based busy poll, the prefer_busy_poll option is hardcoded
to false. Users may want to enable prefer_busy_poll to be used in
conjunction with gro_flush_timeout and defer_hard_irqs_count to keep device
IRQs masked.

Other busy poll methods allow enabling or disabling prefer busy poll via
SO_PREFER_BUSY_POLL, but epoll-based busy polling uses a hardcoded value.

Fix this edge case by adding support for a per-epoll context
prefer_busy_poll option. The default is false, as it was hardcoded before
this change.

Signed-off-by: Joe Damato <[email protected]>
---
fs/eventpoll.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 3985434df527..a69ee11682b9 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -231,6 +231,7 @@ struct eventpoll {
u64 busy_poll_usecs;
/* busy poll packet budget */
u16 busy_poll_budget;
+ bool prefer_busy_poll;
#endif

#ifdef CONFIG_DEBUG_LOCK_ALLOC
@@ -440,13 +441,14 @@ static bool ep_busy_loop(struct eventpoll *ep, int nonblock)
{
unsigned int napi_id = READ_ONCE(ep->napi_id);
u16 budget = READ_ONCE(ep->busy_poll_budget);
+ bool prefer_busy_poll = READ_ONCE(ep->prefer_busy_poll);

if (!budget)
budget = BUSY_POLL_BUDGET;

if ((napi_id >= MIN_NAPI_ID) && ep_busy_loop_on(ep)) {
- napi_busy_loop(napi_id, nonblock ? NULL : ep_busy_loop_end, ep, false,
- budget);
+ napi_busy_loop(napi_id, nonblock ? NULL : ep_busy_loop_end,
+ ep, prefer_busy_poll, budget);
if (ep_events_available(ep))
return true;
/*
@@ -2105,6 +2107,7 @@ static int do_epoll_create(int flags)
#ifdef CONFIG_NET_RX_BUSY_POLL
ep->busy_poll_usecs = 0;
ep->busy_poll_budget = 0;
+ ep->prefer_busy_poll = false;
#endif
ep->file = file;
fd_install(fd, file);
--
2.25.1

2024-02-07 19:05:56

by Jakub Kicinski

Subject: Re: [PATCH net-next v6 3/4] eventpoll: Add per-epoll prefer busy poll option

On Mon, 5 Feb 2024 21:04:48 +0000 Joe Damato wrote:
> When using epoll-based busy poll, the prefer_busy_poll option is hardcoded
> to false. Users may want to enable prefer_busy_poll to be used in
> conjunction with gro_flush_timeout and defer_hard_irqs_count to keep device
> IRQs masked.
>
> Other busy poll methods allow enabling or disabling prefer busy poll via
> SO_PREFER_BUSY_POLL, but epoll-based busy polling uses a hardcoded value.
>
> Fix this edge case by adding support for a per-epoll context
> prefer_busy_poll option. The default is false, as it was hardcoded before
> this change.

Reviewed-by: Jakub Kicinski <[email protected]>

2024-02-08 18:20:36

by Eric Dumazet

Subject: Re: [PATCH net-next v6 3/4] eventpoll: Add per-epoll prefer busy poll option

On Wed, Feb 7, 2024 at 8:04 PM Jakub Kicinski <[email protected]> wrote:
>
> On Mon, 5 Feb 2024 21:04:48 +0000 Joe Damato wrote:
> > When using epoll-based busy poll, the prefer_busy_poll option is hardcoded
> > to false. Users may want to enable prefer_busy_poll to be used in
> > conjunction with gro_flush_timeout and defer_hard_irqs_count to keep device
> > IRQs masked.
> >
> > Other busy poll methods allow enabling or disabling prefer busy poll via
> > SO_PREFER_BUSY_POLL, but epoll-based busy polling uses a hardcoded value.
> >
> > Fix this edge case by adding support for a per-epoll context
> > prefer_busy_poll option. The default is false, as it was hardcoded before
> > this change.
>
> Reviewed-by: Jakub Kicinski <[email protected]>

Reviewed-by: Eric Dumazet <[email protected]>