From: Joel Fernandes <joel@joelfernandes.org>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>,
"David S. Miller" <davem@davemloft.net>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>, Tejun Heo <tj@kernel.org>,
Delyan Kratunov <delyank@fb.com>, linux-mm <linux-mm@kvack.org>,
bpf <bpf@vger.kernel.org>, Kernel Team <kernel-team@fb.com>,
Daniel Bristot de Oliveira <bristot@redhat.com>
Subject: Re: [PATCH v3 bpf-next 09/15] bpf: Batch call_rcu callbacks instead of SLAB_TYPESAFE_BY_RCU.
Date: Wed, 24 Aug 2022 20:49:31 -0400 [thread overview]
Message-ID: <CAEXW_YSa9PhCNv=nmiBtydYhwb+rs-_Wn+0s1zaSvMKjA6=2+Q@mail.gmail.com> (raw)
In-Reply-To: <CAEXW_YSDzfBmHsAtPruRQp6YKA6vXnV4MD3AxsS3=xxWAxuY2g@mail.gmail.com>
On Wed, Aug 24, 2022 at 8:35 PM Joel Fernandes <joel@joelfernandes.org> wrote:
>
> On Wed, Aug 24, 2022 at 8:14 PM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Wed, Aug 24, 2022 at 12:59 PM Kumar Kartikeya Dwivedi
> > <memxor@gmail.com> wrote:
> > >
> > > On Fri, 19 Aug 2022 at 23:43, Alexei Starovoitov
> > > <alexei.starovoitov@gmail.com> wrote:
> > > >
> > > > From: Alexei Starovoitov <ast@kernel.org>
> > > >
> > > > SLAB_TYPESAFE_BY_RCU makes kmem_caches non mergeable and slows down
> > > > kmem_cache_destroy. All bpf_mem_cache are safe to share across different maps
> > > > and programs. Convert SLAB_TYPESAFE_BY_RCU to batched call_rcu. This change
> > > > solves the memory consumption issue, avoids kmem_cache_destroy latency and
> > > > keeps bpf hash map performance the same.
> > > >
> > > > Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> > >
> > > Makes sense, there was a call_rcu_lazy work from Joel (CCed) on doing
> > > this batching using a timer + max batch count instead, I wonder if
> > > that fits our use case and could be useful in the future when it is
> > > merged?
> > >
> > > https://lore.kernel.org/rcu/20220713213237.1596225-2-joel@joelfernandes.org
> >
> > Thanks for the pointer. It looks orthogonal.
> > timer based call_rcu is for power savings.
> > I'm not sure how it would help here. Probably wouldn't hurt.
> > But explicit waiting_for_gp list is necessary here,
> > because two later patches (sleepable support and per-cpu rcu-safe
> > freeing) are relying on this patch.
>
> Hello Kumar and Alexei,
>
> Kumar thanks for the CC. I am seeing this BPF work for the first time
> so have not gone over it too much - but in case the waiting is
> synchronous by any chance, call_rcu_lazy() could hurt. The idea is to
> only queue callbacks that are not all that important to the system
> while keeping it quiet (power being the primary reason but Daniel
> Bristot would concur it brings down OS noise and helps RT as well).
Just as FYI, I see rcu_barrier() used in Alexei's patch - that will
flush the lazy CBs to keep rcu_barrier() both correct and performant.
At that point call_rcu_lazy() is equivalent to call_rcu() as we no
longer kept the callbacks a secret from the rest of the system.
Thanks,
- Joel
next prev parent reply other threads:[~2022-08-25 0:49 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-19 21:42 [PATCH v3 bpf-next 00/15] bpf: BPF specific memory allocator Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 01/15] bpf: Introduce any context " Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 02/15] bpf: Convert hash map to bpf_mem_alloc Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 03/15] selftests/bpf: Improve test coverage of test_maps Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 04/15] samples/bpf: Reduce syscall overhead in map_perf_test Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 05/15] bpf: Relax the requirement to use preallocated hash maps in tracing progs Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 06/15] bpf: Optimize element count in non-preallocated hash map Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 07/15] bpf: Optimize call_rcu " Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 08/15] bpf: Adjust low/high watermarks in bpf_mem_cache Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 09/15] bpf: Batch call_rcu callbacks instead of SLAB_TYPESAFE_BY_RCU Alexei Starovoitov
2022-08-24 19:58 ` Kumar Kartikeya Dwivedi
2022-08-25 0:13 ` Alexei Starovoitov
2022-08-25 0:35 ` Joel Fernandes
2022-08-25 0:49 ` Joel Fernandes [this message]
2022-08-19 21:42 ` [PATCH v3 bpf-next 10/15] bpf: Add percpu allocation support to bpf_mem_alloc Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 11/15] bpf: Convert percpu hash map to per-cpu bpf_mem_alloc Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 12/15] bpf: Remove tracing program restriction on map types Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 13/15] bpf: Prepare bpf_mem_alloc to be used by sleepable bpf programs Alexei Starovoitov
2022-08-19 22:21 ` Kumar Kartikeya Dwivedi
2022-08-19 22:43 ` Alexei Starovoitov
2022-08-19 22:56 ` Kumar Kartikeya Dwivedi
2022-08-19 23:01 ` Alexei Starovoitov
2022-08-24 19:49 ` Kumar Kartikeya Dwivedi
2022-08-25 0:08 ` Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 14/15] bpf: Remove prealloc-only restriction for " Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 15/15] bpf: Introduce sysctl kernel.bpf_force_dyn_alloc Alexei Starovoitov
2022-08-24 20:03 ` [PATCH v3 bpf-next 00/15] bpf: BPF specific memory allocator Kumar Kartikeya Dwivedi
2022-08-25 0:16 ` Alexei Starovoitov
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