From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
To: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
Cc: William Cohen <wcohen@redhat.com>,
systemtap@sourceware.org, Deepak Saxena <dsaxena@linaro.org>
Subject: Re: Re: Regarding systemtap support for AArch64
Date: Mon, 07 Oct 2013 10:11:00 -0000 [thread overview]
Message-ID: <525288DB.5060809@hitachi.com> (raw)
In-Reply-To: <CA+b37P1EQPZZF1AvJc4kYobPrpk1bRzCLA513EUPNX_j=OBYwQ@mail.gmail.com>
(2013/10/07 18:50), Sandeepa Prabhu wrote:
> On 5 October 2013 08:54, Masami Hiramatsu
> <masami.hiramatsu.pt@hitachi.com> wrote:
>> (2013/10/04 12:24), Sandeepa Prabhu wrote:
>>>>>> - Is it really need to use spinlock to protect break_hook?
>>>>> Any cpu can remove breakpoint hooks right, and traversal happen in
>>>>> debug exception context so mutex are not safe (can sleep/schedule out)
>>>>> in debug exception.
>>>>
>>>> I don't think we need to remove the breakpoint hooks after starting
>>>> up the kernel. If we use the spinlock there, we'll pay a big cost
>>>> because of the lock contention.
>>> Not in kprobes. But kgdb can remove breakpoint handler and use same
>>> API. or atleast while providing an api we should not assume race
>>> cannot happen right?
>>
>> In that case, we'd better add a wrapper handler for kgdb so that
>> the list isn't updated even if the kgdb removes its handler.
>>
>>> And there wont be much lock contention, i'ts only if the debug
>>> framework (like kgdb) is wrapping-up, not is normal use-case.
>>
>> Hmm, it seems that the spinlock is locked while handling a breakpoint.
>> This will cause a bad performance issue when we put many kprobes
>> on SMP system.
> arm maintainers prefer a reader/writer spin-locks, so there wont be
> lock contention in debug path, each instance of kprobe hook trap (on
> any CPU) would be a reader, not blocking.
OK for the first step, and it eventually should be fixed to lockless.
(depends on the performance improvement)
>> [...]
>>>>>> - probes-*.c is not good name for the simulator. those should have
>>>>>> better name.
>>>>> May be decode-arm64.c? Originally I had decode-* but the logic is
>>>>> limited to kprobes and uprobes only so renamed that way. Other cases
>>>>> like jump_labels, use different decoding, and may not share same code.
>>>>
>>>> The decoding table will be different from other usecase, but I think
>>>> simulator code can be shared (and must be). It may just get the address,
>>>> instruction, and registers, not the kprobe.
>>> When we wrote at Linaro, our plan was to share simulation calls
>>> between kprobes and uprobes, and planned to use 'struct kprobes' for
>>> both the frameworks, this is how it was done on "arch/arm/kernel/"
>>> effectively.
>>
>> Uh, I should review arm32 again...
>>
>>> If more frameworks can use it (as it seems) I change it to accept
>>> opcode, pc value and saved pt_regs and avoid kprobe struct altogether.
>>> Also, we are starting on uprobes at Linaro, so it won't be too long
>>> before we start thinking about that too ;-)
>>
>> Since kprobes data structure includes many information which is not related
>> to the simulation, I'd like to keep it away from that.
> Yup, can simulate without that. I will avoid kprobe struct from
> simulators and keep it cleaner :-)
Good ;)
[...]
>>> Question:
>>> I am working on v2 patchset based on comments, for next week to post,
>>> do you have basic aarch64 setup (fast-model/hardware), ARM v8-ARM etc?
>>> I mean, how about sharing some efforts with me(Linaro) going further?
>>
>> Yeah, I have a foundation-model simulator, I just need to set it up.
>>
>>> Most work shall go through LAKML so you may have to subscribe to that
>>> ;), but do you mind working on Linaro hosted public git ? we can lay
>>> out a plan then. After kprobes, we have much work on uprobes in queue
>>> (both 32-bit and 64-bit user-space) and your insights help us, since
>>> you are one of the maintainers of both subsystems.
>>
>> Oh, OK. I'll subscribe it, and, yeah, linaro public git should be
>> better place to work with :)
> Thanks!! I will reach out to leads in Linaro regarding read/write
> access and stuff (guess it's read-only right now)
> You can have a look at following Linaro cards (agile projecting tracking):
> https://cards.linaro.org/browse/KWG-13
> https://cards.linaro.org/browse/CARD-564
> If you find them interesting, you may subscribe to these by creating a
> login, and clicking on more -> 'watch this issue'.
Looks nice :) I'll do that.
Thank you!
--
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com
next prev parent reply other threads:[~2013-10-07 10:11 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-24 3:13 Sandeepa Prabhu
2013-09-24 8:43 ` Mark Wielaard
2013-09-24 9:36 ` Sandeepa Prabhu
2013-09-25 18:45 ` William Cohen
2013-09-26 3:13 ` Sandeepa Prabhu
2013-09-26 14:35 ` William Cohen
2013-09-26 14:57 ` Sandeepa Prabhu
2013-09-27 14:16 ` William Cohen
2013-09-30 2:36 ` Masami Hiramatsu
2013-09-30 2:57 ` Sandeepa Prabhu
2013-09-30 12:11 ` William Cohen
2013-10-02 4:17 ` Sandeepa Prabhu
2013-10-02 11:24 ` Masami Hiramatsu
2013-10-03 3:12 ` Sandeepa Prabhu
2013-10-03 13:01 ` Masami Hiramatsu
2013-10-04 3:24 ` Sandeepa Prabhu
2013-10-05 3:24 ` Masami Hiramatsu
2013-10-07 9:51 ` Sandeepa Prabhu
2013-10-07 10:11 ` Masami Hiramatsu [this message]
2013-10-07 11:12 ` Sandeepa Prabhu
2013-10-15 9:39 ` Masami Hiramatsu
2013-10-24 4:26 ` Sandeepa Prabhu
2013-10-24 5:08 ` Masami Hiramatsu
2013-10-04 15:57 ` William Cohen
2013-10-07 9:26 ` Sandeepa Prabhu
2013-10-08 4:28 ` Sandeepa Prabhu
2013-10-08 4:39 ` Sandeepa Prabhu
2013-10-14 16:38 ` William Cohen
2013-10-14 21:21 ` William Cohen
2013-10-15 2:29 ` Sandeepa Prabhu
2013-10-15 3:02 ` William Cohen
2013-10-16 2:33 ` William Cohen
2013-10-16 2:38 ` William Cohen
2013-10-24 1:50 ` William Cohen
2013-10-24 4:19 ` Sandeepa Prabhu
2013-10-24 13:49 ` William Cohen
2013-10-28 14:03 ` William Cohen
2013-11-01 21:06 ` William Cohen
2013-09-25 4:42 ` Masami Hiramatsu
2013-12-02 15:45 ` An attempt for systemtap "make installcheck" AArch64 William Cohen
2013-12-03 5:25 ` Sandeepa Prabhu
2013-12-03 15:21 ` William Cohen
2013-12-03 16:36 ` William Cohen
2013-12-09 20:35 ` William Cohen
2013-12-16 6:06 ` Sandeepa Prabhu
2013-12-16 12:41 ` William Cohen
2013-12-03 19:48 ` William Cohen
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