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From: Denys Vlasenko <vda.linux@googlemail.com>
To: Tejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>,
	Roland McGrath <roland@redhat.com>,
	jan.kratochvil@redhat.com, linux-kernel@vger.kernel.org,
	torvalds@linux-foundation.org, akpm@linux-foundation.org
Subject: Re: [RFC] Proposal for ptrace improvements
Date: Fri, 4 Mar 2011 18:05:08 +0100	[thread overview]
Message-ID: <AANLkTinn_J3fxyjgQk02mHpbxh_5fXNk1qT-YwjgCGqK@mail.gmail.com> (raw)
In-Reply-To: <20110304144059.GS20499@htj.dyndns.org>

On Fri, Mar 4, 2011 at 3:40 PM, Tejun Heo <tj@kernel.org> wrote:
> On Fri, Mar 04, 2011 at 03:31:15PM +0100, Denys Vlasenko wrote:
>> On Fri, Mar 4, 2011 at 3:07 PM, Tejun Heo <tj@kernel.org> wrote:
>> > Hello,
>> >
>> > On Fri, Mar 04, 2011 at 02:59:32PM +0100, Denys Vlasenko wrote:
>> >> I would rather speed strace up than slow it down further, even if
>> >> slightly.
>> >
>> > The question to ask is at what cost?  If mostly unnoticeable slow down
>> > makes the API cleaner, I'll go that way.  Everything is a tradeoff.
>>
>> # time sh -c 'ls -lR /usr/share >/dev/null'
>> real  0m2.633s
>>
>> strace without PTRACE_GETSIGINFO:
>> real  0m47.023s
>> real  0m48.799s
>> real  0m47.695s
>>
>> strace with PTRACE_GETSIGINFO:
>> real  0m51.958s
>> real  0m53.773s
>> real  0m51.625s
>
> Great, numbers, so it's ~10 slow down.  Gees, with or without that
> change, strace(2) is heavy, >18 times slower than without.

Here's a typical sequence of operations strace is doing:

wait4(-1, [{WIFSTOPPED(s) && WSTOPSIG(s) == SIGTRAP}], __WALL, NULL) = 10445
ptrace(PTRACE_GETSIGINFO, 10445, 0, {si_signo=SIGTRAP, si_code=0x5,
si_pid=10445, si_uid=0, si_value={int=0, ptr=0}}) = 0
ptrace(PTRACE_PEEKUSER, 10445, 8*ORIG_RAX, [0x36]) = 0
ptrace(PTRACE_PEEKUSER, 10445, 8*CS, [0x23]) = 0
ptrace(PTRACE_PEEKUSER, 10445, 8*RAX, [0xffffffffffffffda]) = 0
ptrace(PTRACE_PEEKUSER, 10445, 8*RBX, [0x1]) = 0
ptrace(PTRACE_PEEKUSER, 10445, 8*RCX, [0x5401]) = 0
ptrace(PTRACE_PEEKUSER, 10445, 8*RDX, [0xffb83f10]) = 0
ptrace(PTRACE_SYSCALL, 10445, 0x1, SIG_0) = 0

IOW: strace wastes a lot of time just transiting to the kernel and back
with simple syscalls to get the information.

What would help here is a "vectorized" waitpid operation
which retrieves much more information in one go:

waitpid_vec(int max_results, int status_vector[], siginfo_t
si_vector[], struct pt_regs reg_vector[])

-- 
vda

  reply	other threads:[~2011-03-04 17:06 UTC|newest]

Thread overview: 73+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-03-01 15:24 [RFC] Proposal for ptrace improvements Tejun Heo
2011-03-01 16:57 ` Denys Vlasenko
2011-03-01 17:09   ` Tejun Heo
2011-03-01 17:12     ` Tejun Heo
2011-03-01 17:21     ` Denys Vlasenko
2011-03-01 18:34       ` Tejun Heo
2011-03-01 23:51         ` Denys Vlasenko
2011-03-02  7:10           ` Tejun Heo
2011-03-02  5:07         ` Indan Zupancic
2011-03-02  7:44           ` Tejun Heo
2011-03-02 11:32             ` Indan Zupancic
2011-03-02 11:52               ` Denys Vlasenko
2011-03-02 14:50               ` Tejun Heo
2011-03-02 13:32             ` Oleg Nesterov
2011-03-03  0:47               ` Indan Zupancic
2011-03-03  1:30                 ` Denys Vlasenko
2011-03-03  1:55                   ` Indan Zupancic
2011-03-03  7:03                     ` Tejun Heo
2011-03-01 19:06 ` Jan Kratochvil
2011-03-01 22:14   ` Denys Vlasenko
2011-03-02  7:28     ` Tejun Heo
2011-03-02 10:58       ` Denys Vlasenko
2011-03-04 16:14     ` Jan Kratochvil
2011-03-04 16:41       ` Denys Vlasenko
2011-03-04 17:07       ` Oleg Nesterov
2011-03-04 18:12         ` Jan Kratochvil
2011-03-05  8:47           ` Tejun Heo
2011-03-01 22:59 ` Denys Vlasenko
2011-03-02  7:32   ` Tejun Heo
2011-03-02 11:02     ` Denys Vlasenko
2011-03-02 11:23       ` Tejun Heo
2011-03-03 19:26         ` Oleg Nesterov
2011-03-01 23:16 ` Denys Vlasenko
2011-03-02  7:37   ` Tejun Heo
2011-03-02 11:21     ` Denys Vlasenko
2011-03-02 11:27       ` Tejun Heo
2011-03-02 11:48         ` Denys Vlasenko
2011-03-02 14:43           ` Tejun Heo
2011-03-02 15:16             ` Denys Vlasenko
2011-03-02 15:25               ` Tejun Heo
2011-03-03 17:34 ` Oleg Nesterov
2011-03-03 20:22   ` Oleg Nesterov
2011-03-04  8:23     ` Tejun Heo
2011-03-04 18:16       ` Oleg Nesterov
2011-03-05  8:33         ` Tejun Heo
2011-03-04 13:01     ` Denys Vlasenko
2011-03-04 13:41       ` Tejun Heo
2011-03-04 13:59         ` Denys Vlasenko
2011-03-04 14:07           ` Tejun Heo
2011-03-04 14:31             ` Denys Vlasenko
2011-03-04 14:40               ` Tejun Heo
2011-03-04 17:05                 ` Denys Vlasenko [this message]
2011-03-04 17:12                   ` Linus Torvalds
2011-03-04 18:59                     ` Denys Vlasenko
2011-03-04 19:24                       ` Linus Torvalds
2011-03-04 16:13               ` Oleg Nesterov
2011-03-04 16:30                 ` Oleg Nesterov
2011-03-04  8:44   ` Tejun Heo
2011-03-04 16:01     ` Oleg Nesterov
2011-03-04 16:15       ` Tejun Heo
2011-03-04 16:26         ` Oleg Nesterov
2011-03-07 15:08 ` PTRACE_SEIZE/INTERRUPT: " Oleg Nesterov
2011-03-09  9:41   ` Tejun Heo
2011-03-09 17:30     ` Oleg Nesterov
2011-03-07 20:43 ` Roland McGrath
2011-03-09 10:28   ` Tejun Heo
2011-03-10 18:33     ` Steven Rostedt
2011-03-11  8:13       ` Tejun Heo
2011-03-11  8:22       ` Ingo Molnar
2011-03-11  9:35         ` Srikar Dronamraju
2011-03-11  9:43           ` Ingo Molnar
2011-03-14  1:03     ` Frank Ch. Eigler
2011-03-10 15:55   ` Steven Rostedt

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