From: Igor Malovitsa <igor.malovitsa@gmail.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: bpf@vger.kernel.org, daniel@iogearbox.net, andrii@kernel.org,
martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org,
yonghong.song@linux.dev, jolsa@kernel.org, memxor@gmail.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH bpf 1/2] bpf: Load ringbuf consumer_pos under the spinlock
Date: Fri, 16 Oct 2026 19:12:57 +0000 [thread overview]
Message-ID: <atJ3KJn1TVK8Oo-h@corey> (raw)
In-Reply-To: <DM6EA4NZEW6T.1QXD6YWB6J9JZ@gmail.com>
On Fri, Oct 16, 2026 at 16:14:44 +0000, Alexei Starovoitov wrote:
> libbpf writes consumer_pos after every record, so this load is
> a cache miss most of the time.
> Today it's done before the lock. With this patch all other producers
> spin on the lock while this cpu waits for it. On 64-bit too.
> So "Neither changes anything on 64-bit" in the cover letter is not correct.
>
> imo it's not worth slowing down everyone for that.
Thank you for the quick review. I do agree that a bug limited to 32-bit,
requiring 4GB of traffic to reproduce is not worth the trouble.
The reason I raised this patch is building a formal model and
discovering there's technically a bug. If this corner case is
not a concern, I can abandon this patch.
The second patch is zero cost, though.
next prev parent reply other threads:[~2026-10-16 19:13 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-16 0:33 [PATCH bpf 0/2] bpf: Fix ring buffer checks on 32-bit position wrap Igor Malovitsa
2026-10-16 0:33 ` [PATCH bpf 1/2] bpf: Load ringbuf consumer_pos under the spinlock Igor Malovitsa
2026-10-16 16:14 ` Alexei Starovoitov
2026-10-16 19:12 ` Igor Malovitsa [this message]
2026-10-16 0:33 ` [PATCH bpf 2/2] bpf: Fix user ringbuf empty check on 32-bit position wrap Igor Malovitsa
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=atJ3KJn1TVK8Oo-h@corey \
--to=igor.malovitsa@gmail.com \
--cc=alexei.starovoitov@gmail.com \
--cc=andrii@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=eddyz87@gmail.com \
--cc=jolsa@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=martin.lau@linux.dev \
--cc=memxor@gmail.com \
--cc=song@kernel.org \
--cc=yonghong.song@linux.dev \
/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
all inboxes | Powered by JetHome®