BPF Archive on lore.kernel.org
 help / color / Atom feed
From: Stanislav Fomichev <sdf@fomichev.me>
To: Alexei Starovoitov <ast@fb.com>
Cc: Yonghong Song <yhs@fb.com>,
	"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Kernel Team <Kernel-team@fb.com>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH bpf-next v2 0/3] bpf: implement bpf_send_signal() helper
Date: Wed, 22 May 2019 10:11:21 -0700
Message-ID: <20190522171121.GL10244@mini-arch> (raw)
In-Reply-To: <01865520-1963-9acd-b404-8eac03905baf@fb.com>

On 05/22, Alexei Starovoitov wrote:
> On 5/22/19 9:38 AM, Stanislav Fomichev wrote:
> > On 05/21, Yonghong Song wrote:
> >> This patch tries to solve the following specific use case.
> >>
> >> Currently, bpf program can already collect stack traces
> >> through kernel function get_perf_callchain()
> >> when certain events happens (e.g., cache miss counter or
> >> cpu clock counter overflows). But such stack traces are
> >> not enough for jitted programs, e.g., hhvm (jited php).
> >> To get real stack trace, jit engine internal data structures
> >> need to be traversed in order to get the real user functions.
> >>
> >> bpf program itself may not be the best place to traverse
> >> the jit engine as the traversing logic could be complex and
> >> it is not a stable interface either.
> >>
> >> Instead, hhvm implements a signal handler,
> >> e.g. for SIGALARM, and a set of program locations which
> >> it can dump stack traces. When it receives a signal, it will
> >> dump the stack in next such program location.
> >>
> > 
> > [..]
> >> This patch implements bpf_send_signal() helper to send
> >> a signal to hhvm in real time, resulting in intended stack traces.
> > Series looks good. One minor nit/question: maybe rename bpf_send_signal
> > to something like bpf_send_signal_to_current/bpf_current_send_signal/etc?
> > bpf_send_signal is too generic now that you send the signal
> > to the current process..
> 
> bpf_send_signal_to_current was Yonghong's original name
> and I asked him to rename it to bpf_send_signal :)
> I don't see bpf sending signals to arbitrary processes
> in the near future.
:) I was thinking that it might be a bit more clear if we communicate
target process in the name, but I don't feel strongly about it.

So it's not about the future. OTOH, who knows, I remember when people
said there would not be any locking/loops in bpf. And here we are :)

      reply index

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-22  5:39 Yonghong Song
2019-05-22  5:39 ` [PATCH bpf-next v2 1/3] " Yonghong Song
2019-05-23 15:41   ` Daniel Borkmann
2019-05-23 15:58     ` Yonghong Song
2019-05-23 16:28       ` Daniel Borkmann
2019-05-23 21:07         ` Yonghong Song
2019-05-23 21:30           ` Yonghong Song
2019-05-23 23:08             ` Daniel Borkmann
2019-05-23 23:54               ` Yonghong Song
2019-05-24 21:32                 ` Daniel Borkmann
2019-05-22  5:39 ` [PATCH bpf-next v2 2/3] tools/bpf: sync bpf uapi header bpf.h to tools directory Yonghong Song
2019-05-22  5:39 ` [PATCH bpf-next v2 3/3] tools/bpf: add a selftest for bpf_send_signal() helper Yonghong Song
2019-05-22 18:48   ` Andrii Nakryiko
2019-05-22 19:38     ` Yonghong Song
2019-05-22 19:10   ` Stanislav Fomichev
2019-05-22 19:44     ` Yonghong Song
2019-05-22 16:38 ` [PATCH bpf-next v2 0/3] bpf: implement " Stanislav Fomichev
2019-05-22 16:43   ` Alexei Starovoitov
2019-05-22 17:11     ` Stanislav Fomichev [this message]

Reply instructions:

You may reply publically 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=20190522171121.GL10244@mini-arch \
    --to=sdf@fomichev.me \
    --cc=Kernel-team@fb.com \
    --cc=ast@fb.com \
    --cc=bpf@vger.kernel.org \
    --cc=daniel@iogearbox.net \
    --cc=netdev@vger.kernel.org \
    --cc=peterz@infradead.org \
    --cc=yhs@fb.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

BPF Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/bpf/0 bpf/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 bpf bpf/ https://lore.kernel.org/bpf \
		bpf@vger.kernel.org bpf@archiver.kernel.org
	public-inbox-index bpf


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.bpf


AGPL code for this site: git clone https://public-inbox.org/ public-inbox