From: Edward Cree <ecree.xilinx@gmail.com>
To: "Íñigo Huguet" <ihuguet@redhat.com>,
"Jesper Dangaard Brouer" <jbrouer@redhat.com>
Cc: "David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
ivan@cloudflare.com, ast@kernel.org, daniel@iogearbox.net,
hawk@kernel.org, john.fastabend@gmail.com,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
brouer@redhat.com
Subject: Re: [PATCH 1/3] sfc: revert "reduce the number of requested xdp ev queues"
Date: Mon, 12 Jul 2021 15:52:53 +0100 [thread overview]
Message-ID: <681117f7-113b-512d-08c4-0ca7f25a687e@gmail.com> (raw)
In-Reply-To: <CACT4ouf-0AVHvwyPMGN9q-C70Sjm-PFqBnAz7L4rJGKcsVeYXA@mail.gmail.com>
On 12/07/2021 14:40, Íñigo Huguet wrote:
> That's a good idea, which in fact I had already considered, but I had
> (almost) discarded because I still see there 2 problems:
> 1. If there are no free MSI-X vectors remaining at all,
> XDP_TX/REDIRECT will still be disabled.
> 2. If the amount of free MSI-X vectors is little. Then, many CPUs will
> be contending for very few queues/locks, not for normal traffic but
> yes for XDP traffic. If someone wants to intensively use
> XDP_TX/REDIRECT will get a very poor performance, with no option to
> get a better tradeoff between normal and XDP traffic.
[snip]
> So I think that we still need a last resort fallback of sharing TXQs
> with network stack:
> 1. If there are enough resources: 1 queue per CPU for XDP
> 2. If there are not enough resources, but still a fair amount: many
> queues dedicated only to XDP, with (hashed) locking contention
> 3. If there are not free resources, or there are very few: TXQs shared
> for network core and XDP
I think the proper solution to this is to get this policy decision out
of the kernel, and make the allocation of queues be under the control
of userspace. I recall some discussion a couple of years ago about
"making queues a first-class citizen" for the sake of AF_XDP; this
seems to be part and parcel of that.
But I don't know what such an interface would/should look like.
-ed
next prev parent reply other threads:[~2021-07-12 14:52 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-07 8:16 [PATCH 1/3] sfc: revert "reduce the number of requested xdp ev queues" Íñigo Huguet
2021-07-07 8:16 ` [PATCH 2/3] sfc: revert "adjust efx->xdp_tx_queue_count with the real number of initialized queues" Íñigo Huguet
2021-07-07 8:16 ` [PATCH 3/3] sfc: add logs explaining XDP_TX/REDIRECT is not available Íñigo Huguet
2021-07-07 11:23 ` [PATCH 1/3] sfc: revert "reduce the number of requested xdp ev queues" Edward Cree
2021-07-07 11:49 ` Íñigo Huguet
2021-07-07 13:01 ` Martin Habets
2021-07-08 12:14 ` Íñigo Huguet
2021-07-09 14:07 ` Edward Cree
2021-07-09 15:06 ` Jesper Dangaard Brouer
2021-07-12 13:40 ` Íñigo Huguet
2021-07-12 14:52 ` Edward Cree [this message]
2021-07-13 6:20 ` Íñigo Huguet
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