From: Eric Dumazet <edumazet@google.com>
To: Felix Fietkau <nbd@nbd.name>
Cc: netdev@vger.kernel.org, "David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: [RFC v2] net/core: add optional threading for rps backlog processing
Date: Fri, 17 Feb 2023 16:54:11 +0100 [thread overview]
Message-ID: <CANn89i+rCxZgzoM2qJ5yB1NnJoQpovS6_8xdrX5yrxxcC-x9dg@mail.gmail.com> (raw)
In-Reply-To: <b163bfe3-0b91-e2cf-f702-8ab08a30db0d@nbd.name>
On Fri, Feb 17, 2023 at 4:26 PM Felix Fietkau <nbd@nbd.name> wrote:
>
> > Then, process_backlog() has been designed to run only from the cpu
> > tied to the per-cpu data (softnet_data)
> > There are multiple comments about this assumption, and various things
> > that would need to be changed
> > (eg sd_has_rps_ipi_waiting() would be wrong in its current implementation)
> That's why I added the NAPI_STATE_THREADED check in napi_schedule_rps,
> so that sd_has_rps_ipi_waiting would always return false.
> Or are you worried about a race when enabling threading?
>
Please look at all uses of sd->process_queue, without locking. They do
not care about NAPI_STATE_THREADED
flush_backlog() is one instance, but process_backlog() is also using
__skb_dequeue(&sd->process_queue)
I suspect the following patch would work today, and would show
process_queue lock is not used.
diff --git a/net/core/dev.c b/net/core/dev.c
index 5687b528d4c18ef2960edb6bf3161bbad666aece..bed540b417a1b4cd3e384611a4681b8e2a43fd30
100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -11396,7 +11396,7 @@ static int __init net_dev_init(void)
INIT_WORK(flush, flush_backlog);
skb_queue_head_init(&sd->input_pkt_queue);
- skb_queue_head_init(&sd->process_queue);
+ __skb_queue_head_init(&sd->process_queue);
#ifdef CONFIG_XFRM_OFFLOAD
skb_queue_head_init(&sd->xfrm_backlog);
#endif
prev parent reply other threads:[~2023-02-17 15:54 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-17 10:06 [RFC v2] net/core: add optional threading for rps backlog processing Felix Fietkau
2023-02-17 12:23 ` Eric Dumazet
2023-02-17 12:35 ` Felix Fietkau
2023-02-17 12:57 ` Eric Dumazet
2023-02-17 13:40 ` Felix Fietkau
2023-02-17 14:38 ` Eric Dumazet
2023-02-17 15:26 ` Felix Fietkau
2023-02-17 15:54 ` Eric Dumazet [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CANn89i+rCxZgzoM2qJ5yB1NnJoQpovS6_8xdrX5yrxxcC-x9dg@mail.gmail.com \
--to=edumazet@google.com \
--cc=davem@davemloft.net \
--cc=kuba@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=nbd@nbd.name \
--cc=netdev@vger.kernel.org \
--cc=pabeni@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).