netdev - Re: [PATCH v5 bpf-next 00/11] bpf: Introduce BPF timers.

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Date:   Thu, 8 Jul 2021 18:59:49 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
CC:     <davem@...emloft.net>, <daniel@...earbox.net>, <andrii@...nel.org>,
        <netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
        <kernel-team@...com>
Subject: Re: [PATCH v5 bpf-next 00/11] bpf: Introduce BPF timers.

On Wed, Jul 07, 2021 at 06:18:22PM -0700, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@...nel.org>
> 
> The first request to support timers in bpf was made in 2013 before sys_bpf syscall
> was added. That use case was periodic sampling. It was address with attaching
> bpf programs to perf_events. Then during XDP development the timers were requested
> to do garbage collection and health checks. They were worked around by implementing
> timers in user space and triggering progs with BPF_PROG_RUN command.
> The user space timers and perf_event+bpf timers are not armed by the bpf program.
> They're done asynchronously vs program execution. The XDP program cannot send a
> packet and arm the timer at the same time. The tracing prog cannot record an
> event and arm the timer right away. This large class of use cases remained
> unaddressed. The jiffy based and hrtimer based timers are essential part of the
> kernel development and with this patch set the hrtimer based timers will be
> available to bpf programs.
> 
> TLDR: bpf timers is a wrapper of hrtimers with all the extra safety added
> to make sure bpf progs cannot crash the kernel.
Looked more closely from 1-6.  Left minor comments in patch 4.
The later verifier changes make sense to me but I won't be very useful there.

lgtm overall,

Acked-by: Martin KaFai Lau <kafai@...com>