From: David Daney <ddaney@caviumnetworks.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Steven Rostedt <rostedt@goodmis.org>,
Koki Sanagi <sanagi.koki@jp.fujitsu.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@elte.hu>,
Frederic Weisbecker <fweisbec@gmail.com>,
nhorman@tuxdriver.com, scott.a.mcmillan@intel.com,
laijs@cn.fujitsu.com, "H. Peter Anvin" <hpa@zytor.com>,
LKML <linux-kernel@vger.kernel.org>,
eric.dumazet@gmail.com, kaneshige.kenji@jp.fujitsu.com,
David Miller <davem@davemloft.net>,
izumi.taku@jp.fujitsu.com, kosaki.motohiro@jp.fujitsu.com,
Heiko Carstens <heiko.carstens@de.ibm.com>,
"Luck, Tony" <tony.luck@intel.com>
Subject: Re: [PATCH] tracing: Cleanup the convoluted softirq tracepoints
Date: Tue, 19 Oct 2010 14:16:54 -0700 [thread overview]
Message-ID: <4CBE0AC6.3040402@caviumnetworks.com> (raw)
In-Reply-To: <alpine.LFD.2.00.1010191842270.6815@localhost6.localdomain6>
On 10/19/2010 12:49 PM, Thomas Gleixner wrote:
[...]
> So that saves _TWO_ bytes of text and replaces:
>
> - 1e: 83 3d 00 00 00 00 00 cmpl $0x0,0x0(%rip) # 25<test+0x25>
> - 25: 74 4d je 74<test+0x74>
> + 1e: e9 00 00 00 00 jmpq 23<test+0x23>
> + 23: eb 4d jmp 72<test+0x72>
>
> So it trades a conditional vs. two jumps ? WTF ??
>
> I thought that jumplabel magic was supposed to get rid of the jump
> over the tracing code ? In fact it adds another jump. Whatfor ?
The 'asm goto' construct in GCC-4.5 is deficient in this area.
GCC assumes that all exit paths from an 'asm goto' are equally likely,
so the tracing (or dynamic printk etc.) code is assumed to be hot and is
emitted inline. Since they are inline like this, there are all these
jumps around them and they pollute the I-Cache.
I was looking at fixing it, but I think a true general purpose fix would
require enhancing GCC's grammar to allow specifying of the 'likelyness'
of each exit path from 'asm goto'.
David Daney
>
> Now even worse, when you NOP out the jmpq then your tracepoint is
> still not enabled. Brilliant !
>
> Did you guys ever look at the assembly output of that insane shite you
> are advertising with lengthy explanations ?
>
> Obviously _NOT_
>
> Come back when you can show me a clean imlementation of all this crap
> which reproduces with my jumplabel enabled stock compiler. And please
> just send me a patch w/o the blurb.
>
> And sane looks like:
>
> jmpq 2f<---- This gets noped out
> 1:
> mov %r12,%rdi
> callq *(%r12)
> [whatever cleanup it takes ]
> leaveq
> retq
>
> 2f:
> [tracing gunk]
> jmp 1b
>
> And further I want to see the tracing gunk in a minimal size so the
> net/core/dev.c deinlining does not happen.
>
> Thanks,
>
> tglx
>
> P.S.: It might be helpful and polite if you'd take off your tracing
> blinkers from time to time.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
>
next prev parent reply other threads:[~2010-10-19 21:17 UTC|newest]
Thread overview: 93+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-23 9:41 [PATCH v4 0/5] netdev: show a process of packets Koki Sanagi
2010-08-23 9:42 ` [PATCH v4 1/5] irq: add tracepoint to softirq_raise Koki Sanagi
2010-09-03 15:29 ` Frederic Weisbecker
2010-09-03 15:39 ` Steven Rostedt
2010-09-03 15:42 ` Frederic Weisbecker
2010-09-03 15:43 ` Steven Rostedt
2010-09-03 15:50 ` Frederic Weisbecker
2010-09-06 1:46 ` Koki Sanagi
2010-09-08 8:33 ` [tip:perf/core] irq: Add " tip-bot for Lai Jiangshan
2010-09-08 11:25 ` [sparc build bug] " Ingo Molnar
2010-09-08 12:26 ` [PATCH] irq: Fix circular headers dependency Frederic Weisbecker
2010-09-09 19:54 ` [tip:perf/core] " tip-bot for Frederic Weisbecker
2010-10-18 9:44 ` [sparc build bug] Re: [tip:perf/core] irq: Add tracepoint to softirq_raise Peter Zijlstra
2010-10-18 10:11 ` Peter Zijlstra
2010-10-18 10:26 ` Heiko Carstens
2010-10-18 10:48 ` Peter Zijlstra
2010-10-19 10:58 ` Koki Sanagi
2010-10-19 11:25 ` Peter Zijlstra
2010-10-19 13:00 ` [PATCH] tracing: Cleanup the convoluted softirq tracepoints Thomas Gleixner
2010-10-19 13:08 ` Peter Zijlstra
2010-10-19 13:22 ` Mathieu Desnoyers
2010-10-19 13:41 ` Thomas Gleixner
2010-10-19 13:54 ` Steven Rostedt
2010-10-19 14:07 ` Thomas Gleixner
2010-10-19 14:28 ` Mathieu Desnoyers
2010-10-19 19:49 ` Thomas Gleixner
2010-10-19 20:55 ` Steven Rostedt
2010-10-19 21:07 ` Thomas Gleixner
2010-10-19 21:23 ` Steven Rostedt
2010-10-19 21:48 ` H. Peter Anvin
2010-10-19 22:23 ` Steven Rostedt
2010-10-19 22:26 ` H. Peter Anvin
2010-10-19 22:27 ` Peter Zijlstra
2010-10-19 23:39 ` H. Peter Anvin
2010-10-19 23:45 ` Steven Rostedt
2010-10-20 0:43 ` Jason Baron
2010-10-19 22:41 ` Mathieu Desnoyers
2010-10-19 22:49 ` H. Peter Anvin
2010-10-19 23:05 ` Steven Rostedt
2010-10-19 23:09 ` H. Peter Anvin
2010-10-20 15:27 ` Jason Baron
2010-10-20 15:41 ` Mathieu Desnoyers
2010-10-25 21:54 ` H. Peter Anvin
2010-10-25 22:01 ` Mathieu Desnoyers
2010-10-25 22:12 ` H. Peter Anvin
2010-10-25 22:19 ` H. Peter Anvin
2010-10-25 22:55 ` Mathieu Desnoyers
2010-10-26 0:39 ` Steven Rostedt
2010-10-26 1:14 ` Mathieu Desnoyers
2010-10-19 22:04 ` Thomas Gleixner
2010-10-19 22:33 ` Steven Rostedt
2010-10-21 16:18 ` Thomas Gleixner
2010-10-21 17:05 ` Steven Rostedt
2010-10-21 19:56 ` Thomas Gleixner
2010-10-25 22:31 ` H. Peter Anvin
2010-10-19 21:45 ` Thomas Gleixner
2010-10-19 22:14 ` Steven Rostedt
2010-10-19 21:16 ` David Daney [this message]
2010-10-19 21:32 ` Jason Baron
2010-10-19 21:38 ` David Daney
2010-10-19 21:47 ` Steven Rostedt
2010-10-19 21:28 ` Jason Baron
2010-10-19 21:55 ` Thomas Gleixner
2010-10-19 22:17 ` Thomas Gleixner
2010-10-20 1:36 ` Steven Rostedt
2010-10-20 1:52 ` Jason Baron
2010-10-25 22:32 ` H. Peter Anvin
2010-10-19 22:38 ` Jason Baron
2010-10-19 22:44 ` H. Peter Anvin
2010-10-19 22:56 ` Steven Rostedt
2010-10-19 22:57 ` H. Peter Anvin
2010-10-19 14:46 ` Steven Rostedt
2010-10-19 14:00 ` Mathieu Desnoyers
2010-10-21 14:52 ` [tip:perf/core] " tip-bot for Thomas Gleixner
2010-08-23 9:43 ` [PATCH v4 2/5] napi: convert trace_napi_poll to TRACE_EVENT Koki Sanagi
2010-08-24 3:52 ` David Miller
2010-09-08 8:34 ` [tip:perf/core] napi: Convert " tip-bot for Neil Horman
2010-08-23 9:45 ` [PATCH v4 3/5] netdev: add tracepoints to netdev layer Koki Sanagi
2010-08-24 3:53 ` David Miller
2010-09-08 8:34 ` [tip:perf/core] netdev: Add " tip-bot for Koki Sanagi
2010-08-23 9:46 ` [PATCH v4 4/5] skb: add tracepoints to freeing skb Koki Sanagi
2010-08-24 3:53 ` David Miller
2010-09-08 8:35 ` [tip:perf/core] skb: Add " tip-bot for Koki Sanagi
2010-08-23 9:47 ` [PATCH v4 5/5] perf:add a script shows a process of packet Koki Sanagi
2010-08-24 3:53 ` David Miller
2010-09-07 16:57 ` Frederic Weisbecker
2010-09-08 8:35 ` [tip:perf/core] perf: Add a script to show packets processing tip-bot for Koki Sanagi
2010-08-30 23:50 ` [PATCH v4 0/5] netdev: show a process of packets Steven Rostedt
2010-09-03 2:10 ` Koki Sanagi
2010-09-03 2:17 ` David Miller
2010-09-03 2:55 ` Koki Sanagi
2010-09-03 4:46 ` Frederic Weisbecker
2010-09-03 5:12 ` Koki Sanagi
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