From: Peter Zijlstra <peterz@infradead.org>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
davem@davemloft.net, daniel@iogearbox.net,
jakub.kicinski@netronome.com, netdev@vger.kernel.org,
kernel-team@fb.com, mingo@redhat.com, will.deacon@arm.com,
Paul McKenney <paulmck@linux.vnet.ibm.com>,
jannh@google.com
Subject: Re: bpf memory model. Was: [PATCH v4 bpf-next 1/9] bpf: introduce bpf_spin_lock
Date: Tue, 29 Jan 2019 10:16:54 +0100 [thread overview]
Message-ID: <20190129091654.GD28485@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190128215623.6eqskzhklydhympa@ast-mbp>
On Mon, Jan 28, 2019 at 01:56:24PM -0800, Alexei Starovoitov wrote:
> On Mon, Jan 28, 2019 at 10:24:08AM +0100, Peter Zijlstra wrote:
> > Ah, but the loop won't be in the BPF program itself. The BPF program
> > would only have had the BPF_SPIN_LOCK instruction, the JIT them emits
> > code similar to queued_spin_lock()/queued_spin_unlock() (or calls to
> > out-of-line versions of them).
>
> As I said we considered exactly that and such approach has a lot of downsides
> comparing with the helper approach.
> Pretty much every time new feature is added we're evaluating whether it
> should be new instruction or new helper. 99% of the time we go with new helper.
Ah; it seems I'm confused on helper vs instruction. As in, I've no idea
what a helper is.
> > There isn't anything that mandates the JIT uses the exact same locking
> > routines the interpreter does, is there?
>
> sure. This bpf_spin_lock() helper can be optimized whichever way the kernel wants.
> Like bpf_map_lookup_elem() call is _inlined_ by the verifier for certain map types.
> JITs don't even need to do anything. It looks like function call from bpf prog
> point of view, but in JITed code it is a sequence of native instructions.
>
> Say tomorrow we find out that bpf_prog->bpf_spin_lock()->queued_spin_lock()
> takes too much time then we can inline fast path of queued_spin_lock
> directly into bpf prog and save function call cost.
OK, so then the JIT can optimize helpers. Would it not make sense to
have the simple test-and-set spinlock in the generic code and have the
JITs use arch_spinlock_t where appropriate?
next prev parent reply other threads:[~2019-01-29 9:17 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-24 4:13 [PATCH v4 bpf-next 0/9] introduce bpf_spin_lock Alexei Starovoitov
2019-01-24 4:13 ` [PATCH v4 bpf-next 1/9] bpf: " Alexei Starovoitov
2019-01-24 18:01 ` Peter Zijlstra
2019-01-24 18:56 ` Peter Zijlstra
2019-01-24 23:42 ` Paul E. McKenney
2019-01-25 0:05 ` Alexei Starovoitov
2019-01-25 1:22 ` Paul E. McKenney
2019-01-25 1:46 ` Jann Horn
2019-01-25 2:38 ` Alexei Starovoitov
2019-01-25 4:27 ` Alexei Starovoitov
2019-01-25 4:31 ` Paul E. McKenney
2019-01-25 4:47 ` Alexei Starovoitov
2019-01-25 16:02 ` Paul E. McKenney
2019-01-25 4:11 ` Paul E. McKenney
2019-01-25 16:18 ` Jann Horn
2019-01-25 22:51 ` Paul E. McKenney
2019-01-25 23:44 ` Alexei Starovoitov
2019-01-26 0:43 ` Jann Horn
2019-01-26 0:59 ` Jann Horn
2019-01-24 23:58 ` Alexei Starovoitov
2019-01-25 0:18 ` Jann Horn
2019-01-25 2:49 ` Alexei Starovoitov
2019-01-25 2:29 ` Eric Dumazet
2019-01-25 2:34 ` Alexei Starovoitov
2019-01-25 2:44 ` Eric Dumazet
2019-01-25 2:57 ` Alexei Starovoitov
2019-01-25 8:38 ` Peter Zijlstra
2019-01-25 9:10 ` Peter Zijlstra
2019-01-25 23:42 ` Alexei Starovoitov
2019-01-28 8:24 ` Peter Zijlstra
2019-01-28 8:31 ` Peter Zijlstra
2019-01-28 8:35 ` Peter Zijlstra
2019-01-28 20:49 ` Alexei Starovoitov
2019-01-28 8:43 ` Peter Zijlstra
2019-01-28 21:37 ` Alexei Starovoitov
2019-01-29 8:59 ` Peter Zijlstra
2019-01-30 2:20 ` Alexei Starovoitov
2019-01-25 9:59 ` Peter Zijlstra
2019-01-25 10:09 ` Peter Zijlstra
2019-01-25 10:23 ` Peter Zijlstra
2019-01-26 0:17 ` bpf memory model. Was: " Alexei Starovoitov
2019-01-28 9:24 ` Peter Zijlstra
2019-01-28 21:56 ` Alexei Starovoitov
2019-01-29 9:16 ` Peter Zijlstra [this message]
2019-01-30 2:32 ` Alexei Starovoitov
2019-01-30 8:58 ` Peter Zijlstra
2019-01-30 19:36 ` Alexei Starovoitov
2019-01-30 18:11 ` Will Deacon
2019-01-30 18:36 ` Paul E. McKenney
2019-01-30 19:51 ` Alexei Starovoitov
2019-01-30 21:05 ` Paul E. McKenney
2019-01-30 22:57 ` Alexei Starovoitov
2019-01-31 14:01 ` Paul E. McKenney
2019-01-31 18:47 ` Alexei Starovoitov
2019-02-01 14:05 ` Paul E. McKenney
2019-01-30 19:50 ` Alexei Starovoitov
2019-01-24 4:13 ` [PATCH v4 bpf-next 2/9] bpf: add support for bpf_spin_lock to cgroup local storage Alexei Starovoitov
2019-01-24 4:13 ` [PATCH v4 bpf-next 3/9] tools/bpf: sync include/uapi/linux/bpf.h Alexei Starovoitov
2019-01-24 4:13 ` [PATCH v4 bpf-next 4/9] selftests/bpf: add bpf_spin_lock tests Alexei Starovoitov
2019-01-24 4:13 ` [PATCH v4 bpf-next 5/9] selftests/bpf: add bpf_spin_lock C test Alexei Starovoitov
2019-01-24 4:14 ` [PATCH v4 bpf-next 6/9] bpf: introduce BPF_F_LOCK flag Alexei Starovoitov
2019-01-24 4:14 ` [PATCH v4 bpf-next 7/9] tools/bpf: sync uapi/bpf.h Alexei Starovoitov
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=20190129091654.GD28485@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=alexei.starovoitov@gmail.com \
--cc=ast@kernel.org \
--cc=daniel@iogearbox.net \
--cc=davem@davemloft.net \
--cc=jakub.kicinski@netronome.com \
--cc=jannh@google.com \
--cc=kernel-team@fb.com \
--cc=mingo@redhat.com \
--cc=netdev@vger.kernel.org \
--cc=paulmck@linux.vnet.ibm.com \
--cc=will.deacon@arm.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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.