From: Jakub Kicinski <kuba@kernel.org>
To: Joe Damato <jdamato@fastly.com>
Cc: "Samudrala, Sridhar" <sridhar.samudrala@intel.com>,
Eric Dumazet <edumazet@google.com>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
chuck.lever@oracle.com, jlayton@kernel.org,
linux-api@vger.kernel.org, brauner@kernel.org,
davem@davemloft.net, alexander.duyck@gmail.com,
Wei Wang <weiwan@google.com>,
Amritha Nambiar <amritha.nambiar@intel.com>
Subject: Re: [net-next 0/3] Per epoll context busy poll support
Date: Mon, 5 Feb 2024 11:59:55 -0800 [thread overview]
Message-ID: <20240205115955.5cde5a13@kernel.org> (raw)
In-Reply-To: <20240205185130.GB10463@fastly.com>
On Mon, 5 Feb 2024 10:51:30 -0800 Joe Damato wrote:
> > We reused the gro_flush_timeout as an existing "user doesn't care if
> > packets get delayed by this much in worst case" value. If you set
> > SO_PREFER_BUSY_POLL the next time you busy pool the NAPI will be marked
> > as "already scheduled" and a timer is set (to gro_flush_timeout).
> > If NIC IRQ fires before gro_flush_timeout it gets ignored, because NAPI
> > is already marked as scheduled.
> > If you busy poll again the timer gets postponed for another
> > gro_flush_timeout nsec.
> > If timer fires we go back to normal NAPI processing.
>
> Ah, I see. From my reading of the code in busy_poll_stop (which could be
> wrong), defer_hard_irqs_count must also be non-zero to postpone the timer.
>
> Is that right?
>
> If so, I think the tricky thing with this is that these settings are
> system-wide, so they'd affect non-busy poll apps, too.
>
> I think in the ideal case being able to set these on a per-NAPI basis would
> be very helpful. Maybe something for me to try working on next.
If wonder if it'd be good enough to do:
min(defer_hard_irqs_count, 1)
there. If caller asked to prefer busy poll they clearly want to poll.
An explicit per-NAPI API works too, but it's a bit more work.
If I was doing the work I'd try min(..., 1) with the workload.
If there's value in having the full config - go for it.
prev parent reply other threads:[~2024-02-05 19:59 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-24 2:53 [net-next 0/3] Per epoll context busy poll support Joe Damato
2024-01-24 2:53 ` [net-next 1/3] eventpoll: support busy poll per epoll instance Joe Damato
2024-01-24 2:53 ` [net-next 2/3] eventpoll: Add per-epoll busy poll packet budget Joe Damato
2024-01-24 2:53 ` [net-next 3/3] eventpoll: Add epoll ioctl for epoll_params Joe Damato
2024-01-24 15:37 ` Joe Damato
2024-01-24 8:20 ` [net-next 0/3] Per epoll context busy poll support Eric Dumazet
2024-01-24 14:20 ` Joe Damato
2024-01-24 14:38 ` Eric Dumazet
2024-01-24 15:19 ` Joe Damato
2024-01-30 18:54 ` Samudrala, Sridhar
2024-02-02 3:28 ` Joe Damato
2024-02-02 17:23 ` Samudrala, Sridhar
2024-02-02 18:22 ` Jakub Kicinski
2024-02-02 19:33 ` Joe Damato
2024-02-02 19:58 ` Jakub Kicinski
2024-02-02 20:23 ` Joe Damato
2024-02-02 20:50 ` Samudrala, Sridhar
2024-02-02 20:55 ` Joe Damato
2024-02-03 1:15 ` Jakub Kicinski
2024-02-05 18:17 ` Stanislav Fomichev
2024-02-05 18:52 ` Joe Damato
2024-02-05 19:48 ` Jakub Kicinski
2024-02-05 18:51 ` Joe Damato
2024-02-05 19:59 ` Jakub Kicinski [this message]
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