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From:   Andy Lutomirski <luto@amacapital.net>
Mime-Version: 1.0 (1.0)
Subject: Re: Why do kprobes and uprobes singlestep?
Date:   Tue, 2 Mar 2021 17:46:32 -0800
Message-Id: <968E85AE-75B8-42D7-844A-0D61B32063B3@amacapital.net>
References: <CAADnVQJtpvB8wDFv46O0GEaHkwmT1Ea70BJfgS36kDX0u4uZ-g@mail.gmail.com>
Cc:     Andy Lutomirski <luto@kernel.org>, bpf <bpf@vger.kernel.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
        "David S. Miller" <davem@davemloft.net>, X86 ML <x86@kernel.org>,
        Andrew Cooper <andrew.cooper3@citrix.com>
In-Reply-To: <CAADnVQJtpvB8wDFv46O0GEaHkwmT1Ea70BJfgS36kDX0u4uZ-g@mail.gmail.com>
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Precedence: bulk


> On Mar 2, 2021, at 5:22 PM, Alexei Starovoitov <alexei.starovoitov@gmail.c=
om> wrote:
>=20
> =EF=BB=BFOn Tue, Mar 2, 2021 at 1:02 PM Andy Lutomirski <luto@amacapital.n=
et> wrote:
>>=20
>>=20
>>>> On Mar 2, 2021, at 12:24 PM, Alexei Starovoitov <alexei.starovoitov@gma=
il.com> wrote:
>>>=20
>>> =EF=BB=BFOn Tue, Mar 2, 2021 at 10:38 AM Andy Lutomirski <luto@kernel.or=
g> wrote:
>>>>=20
>>>> Is there something like a uprobe test suite?  How maintained /
>>>> actively used is uprobe?
>>>=20
>>> uprobe+bpf is heavily used in production.
>>> selftests/bpf has only one test for it though.
>>>=20
>>> Why are you asking?
>>=20
>> Because the integration with the x86 entry code is a mess, and I want to k=
now whether to mark it BROKEN or how to make sure the any cleanups actually w=
ork.
>=20
> Any test case to repro the issue you found?
> Is it a bug or just messy code?

Just messy code.

> Nowadays a good chunk of popular applications (python, mysql, etc) has
> USDTs in them.
> Issues reported with bcc:
> https://github.com/iovisor/bcc/issues?q=3Dis%3Aissue+USDT
> Similar thing with bpftrace.
> Both standard USDT and semaphore based are used in the wild.
> uprobe for containers has been a long standing feature request.
> If you can improve uprobe performance that would be awesome.
> That's another thing that people report often. We optimized it a bit.
> More can be done.


Wait... USDT is much easier to implement well.  Are we talking just USDT or a=
re we talking about general uprobes in which almost any instruction can get p=
robed?  If the only users that care about uprobes are doing USDT, we could v=
astly simplify the implementation and probably make it faster, too.=