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From: Jesper Dangaard Brouer <brouer@redhat.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: "Toke Høiland-Jørgensen" <toke@redhat.com>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Martin KaFai Lau" <kafai@fb.com>,
	"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
	"Marek Majkowski" <marek@cloudflare.com>,
	"Lorenz Bauer" <lmb@cloudflare.com>,
	"Alan Maguire" <alan.maguire@oracle.com>,
	"David Miller" <davem@davemloft.net>,
	netdev@vger.kernel.org, bpf@vger.kernel.org, brouer@redhat.com
Subject: Re: [PATCH bpf-next v3 1/5] bpf: Support chain calling multiple BPF programs after each other
Date: Wed, 9 Oct 2019 12:19:55 +0200	[thread overview]
Message-ID: <20191009121955.29cad5bb@carbon> (raw)
In-Reply-To: <20191009015117.pldowv6n3k5p3ghr@ast-mbp.dhcp.thefacebook.com>

On Tue, 8 Oct 2019 18:51:19 -0700
Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:

> On Tue, Oct 08, 2019 at 10:07:46AM +0200, Toke Høiland-Jørgensen wrote:
> > Alexei Starovoitov <alexei.starovoitov@gmail.com> writes:
> >   
> > > On Mon, Oct 07, 2019 at 07:20:36PM +0200, Toke Høiland-Jørgensen wrote:  
> > >> From: Toke Høiland-Jørgensen <toke@redhat.com>
> > >> 
> > >> This adds support for wrapping eBPF program dispatch in chain calling
> > >> logic. The code injection is controlled by a flag at program load time; if
> > >> the flag is set, the BPF program will carry a flag bit that changes the
> > >> program dispatch logic to wrap it in a chain call loop.
[...]
> > >> diff --git a/include/linux/filter.h b/include/linux/filter.h
> > >> index 2ce57645f3cd..3d1e4991e61d 100644
> > >> --- a/include/linux/filter.h
> > >> +++ b/include/linux/filter.h
[...]
> > >>  #define BPF_PROG_RUN(prog, ctx)	({				\
> > >> @@ -559,14 +585,18 @@ DECLARE_STATIC_KEY_FALSE(bpf_stats_enabled_key);
> > >>  	if (static_branch_unlikely(&bpf_stats_enabled_key)) {	\
> > >>  		struct bpf_prog_stats *stats;			\
> > >>  		u64 start = sched_clock();			\
> > >> -		ret = (*(prog)->bpf_func)(ctx, (prog)->insnsi);	\
> > >> +		ret = prog->chain_calls ?			\
> > >> +			do_chain_calls(prog, ctx) :			\
> > >> +			 (*(prog)->bpf_func)(ctx, (prog)->insnsi);	\  
> > >
> > > I thought you agreed on 'no performance regressions' rule?  
> > 
> > As I wrote in the cover letter I could not measurable a performance
> > impact from this, even with the simplest possible XDP program (where
> > program setup time has the largest impact).
> > 
> > This was the performance before/after patch (also in the cover letter):
> > 
> > Before patch (XDP DROP program):  31.5 Mpps
> > After patch (XDP DROP program):   32.0 Mpps
> > 
> > So actually this *increases* performance ;)
> > (Or rather, the difference is within the measurement uncertainty on my
> > system).  
> 
> I have hard time believing such numbers.

Don't look at this as +/- 500Kpps.  Instead you have to realize that the
performance difference in ns (nano-seconds) is only 0.5 ns (0.496 ns).

 (1/31.5*1000)-(1/32.0*1000) = 0.4960 ns

This "half-a-nanosec" is below the measurement uncertainty of any
system. My system have approx 2-3 ns measurement variance, which I'm
proud of.  At these speeds (32Mpps) this e.g. 3 ns variance would
result in -2.8 Mpps (29.2Mpps).


The change Toke did in BPF_PROG_RUN does not introduce any measurable
performance change, as least on high-end Intel CPUs.  This DOES satisfy
'no performance regressions' rule.  You can dislike the solution for
other reasons ;-)

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

  parent reply	other threads:[~2019-10-09 10:20 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-07 17:20 [PATCH bpf-next v3 0/5] xdp: Support multiple programs on a single interface through chain calls Toke Høiland-Jørgensen
2019-10-07 17:20 ` [PATCH bpf-next v3 1/5] bpf: Support chain calling multiple BPF programs after each other Toke Høiland-Jørgensen
2019-10-07 20:42   ` Alexei Starovoitov
2019-10-08  8:07     ` Toke Høiland-Jørgensen
2019-10-09  1:51       ` Alexei Starovoitov
2019-10-09  8:03         ` Toke Høiland-Jørgensen
2019-10-10  4:41           ` Alexei Starovoitov
2019-10-14 12:35             ` Toke Høiland-Jørgensen
2019-10-14 17:08               ` John Fastabend
2019-10-14 18:48                 ` Toke Høiland-Jørgensen
2019-10-15 16:30                   ` Edward Cree
2019-10-15 16:42                     ` Toke Høiland-Jørgensen
2019-10-15 18:33                       ` Edward Cree
2019-10-17 12:11                         ` Toke Høiland-Jørgensen
2019-10-22 17:27                           ` Edward Cree
2019-10-22 18:07                             ` Toke Høiland-Jørgensen
2019-11-12  2:51                               ` static and dynamic linking. Was: [PATCH bpf-next v3 1/5] bpf: Support chain calling multiple BPF Alexei Starovoitov
2019-11-12 16:20                                 ` Toke Høiland-Jørgensen
2019-11-12 19:52                                   ` Alexei Starovoitov
2019-11-12 21:25                                     ` Edward Cree
2019-11-12 23:18                                       ` Alexei Starovoitov
2019-11-13 18:30                                         ` Edward Cree
2019-11-13 18:51                                           ` Andrii Nakryiko
2019-11-15  2:13                                           ` Alexei Starovoitov
2019-11-15 16:56                                             ` John Fastabend
2019-11-12 23:25                                     ` John Fastabend
2019-11-13  0:21                                       ` Alexei Starovoitov
2019-11-13  5:33                                         ` John Fastabend
2019-11-15  1:50                                           ` Alexei Starovoitov
2019-11-15 16:39                                             ` John Fastabend
2019-11-14 15:41                                     ` Toke Høiland-Jørgensen
2019-11-12 16:32                                 ` Edward Cree
2019-11-15 11:48                                 ` Lorenz Bauer
2019-11-15 23:02                                   ` Alexei Starovoitov
2019-11-18 13:29                                     ` Lorenz Bauer
2019-10-21 23:51                         ` [PATCH bpf-next v3 1/5] bpf: Support chain calling multiple BPF programs after each other Edward Cree
2019-10-16  2:28               ` Alexei Starovoitov
2019-10-16  8:27                 ` Jesper Dangaard Brouer
2019-10-16 10:35                   ` Daniel Borkmann
2019-10-16 11:16                     ` Toke Høiland-Jørgensen
2019-10-16 13:51                 ` Toke Høiland-Jørgensen
2019-10-19 20:09                   ` bpf indirect calls Alexei Starovoitov
2019-10-20 10:58                     ` Toke Høiland-Jørgensen
2019-10-25 16:30                       ` Alexei Starovoitov
2019-10-27 12:15                         ` Toke Høiland-Jørgensen
2019-10-09 10:19         ` Jesper Dangaard Brouer [this message]
2019-10-09 17:57           ` [PATCH bpf-next v3 1/5] bpf: Support chain calling multiple BPF programs after each other Alexei Starovoitov
2019-10-07 17:20 ` [PATCH bpf-next v3 2/5] bpf: Add support for setting chain call sequence for programs Toke Høiland-Jørgensen
2019-10-07 20:38   ` Daniel Borkmann
2019-10-08  8:09     ` Toke Høiland-Jørgensen
2019-10-07 17:20 ` [PATCH bpf-next v3 3/5] tools: Update bpf.h header for program chain calls Toke Høiland-Jørgensen
2019-10-07 17:20 ` [PATCH bpf-next v3 4/5] libbpf: Add syscall wrappers for BPF_PROG_CHAIN_* commands Toke Høiland-Jørgensen
2019-10-07 17:20 ` [PATCH bpf-next v3 5/5] selftests: Add tests for XDP chain calls Toke Høiland-Jørgensen
2019-10-07 18:58 ` [PATCH bpf-next v3 0/5] xdp: Support multiple programs on a single interface through " John Fastabend
2019-10-08  8:42   ` Toke Høiland-Jørgensen

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