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Message-ID: <48D84A2A.2030009@ct.jp.nec.com>
Date: Mon, 22 Sep 2008 18:45:14 -0700
From: Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
To: Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
"H. Peter Anvin" <hpa@...or.com>
Cc: linux-kernel@...r.kernel.org
Subject: [RFC PATCH -tip 0/4] x86: signal handler improvement
This patch series is experimental.
I made it against tip/master.
I noticed there are inefficient codes in x86 signals.
For example, disassembled 32-bit setup_sigcontext();
0000007c <setup_sigcontext>:
7c: 55 push %ebp
7d: 89 e5 mov %esp,%ebp
7f: 57 push %edi
80: 31 ff xor %edi,%edi
82: 56 push %esi
83: 89 c6 mov %eax,%esi
85: 53 push %ebx
86: 83 ec 58 sub $0x58,%esp
89: 89 55 a4 mov %edx,-0x5c(%ebp)
8c: 89 fa mov %edi,%edx
8e: 8b 41 24 mov 0x24(%ecx),%eax
91: 89 46 04 mov %eax,0x4(%esi)
94: 89 55 a8 mov %edx,-0x58(%ebp)
...
184: 8b 5d ac mov -0x54(%ebp),%ebx
187: 0b 5d a8 or -0x58(%ebp),%ebx
18a: 0b 5d b0 or -0x50(%ebp),%ebx
18d: 0b 5d b4 or -0x4c(%ebp),%ebx
190: 0b 5d b8 or -0x48(%ebp),%ebx
193: 0b 5d bc or -0x44(%ebp),%ebx
196: 0b 5d c0 or -0x40(%ebp),%ebx
199: 0b 5d c4 or -0x3c(%ebp),%ebx
19c: 0b 5d c8 or -0x38(%ebp),%ebx
19f: 0b 5d cc or -0x34(%ebp),%ebx
1a2: 0b 5d d0 or -0x30(%ebp),%ebx
1a5: 0b 5d d4 or -0x2c(%ebp),%ebx
1a8: 0b 5d d8 or -0x28(%ebp),%ebx
1ab: 0b 5d dc or -0x24(%ebp),%ebx
1ae: 0b 5d e0 or -0x20(%ebp),%ebx
1b1: 0b 5d e4 or -0x1c(%ebp),%ebx
1b4: 0b 5d e8 or -0x18(%ebp),%ebx
1b7: 0b 5d ec or -0x14(%ebp),%ebx
1ba: 0b 5d f0 or -0x10(%ebp),%ebx
1bd: 09 fb or %edi,%ebx
...
1dc: 09 d8 or %ebx,%eax
1de: 5b pop %ebx
1df: 09 c8 or %ecx,%eax
1e1: 5e pop %esi
1e2: 5f pop %edi
1e3: 5d pop %ebp
1e4: c3 ret
there is a lot of "or" operation with stack, and it came from a set of
following lines;
err |= __put_user(x, ptr);
The above line compiled to like this;
a0: 89 fa mov %edi,%edx
a2: 8b 41 20 mov 0x20(%ecx),%eax
a5: 89 46 08 mov %eax,0x8(%esi)
a8: 89 55 b0 mov %edx,-0x50(%ebp)
and errors in __put_user is stored to stack.
At the end of function, all errors in stack are calculated. If access to user
space is failed, %edx is set to -EFAULT in exception handler and stored to
stack for later operation.
It seems inefficient.
This patch series introduce __{put|get}_user_cerr for cumulative error
handling. So, the line;
err |= __put_user(x, ptr);
changes to
__put_user_cerr(x, ptr, err);
and it compiled to like this;
92: 8b 41 20 mov 0x20(%ecx),%eax
95: 89 47 08 mov %eax,0x8(%edi)
The cumulative error is kept in the other register, in this example,
%esi is used for this, and returns it. If access to user space causes fault,
%esi is set to the value (%esi | -EFAULT) in exception handler.
137: 89 f0 mov %esi,%eax
139: 5b pop %ebx
13a: 5e pop %esi
13b: 5f pop %edi
13c: 5d pop %ebp
13d: c3 ret
The results of this, I got a little performance improvement in signal
handling. Here is a result of lmbench.
I've tried 64-bit only at this time. Will measure on 32-bit.
Processor, Processes - times in microseconds - smaller is better
------------------------------------------------------------------------------
Host OS Mhz null null open slct sig sig fork exec sh
call I/O stat clos TCP inst hndl proc proc proc
--------- ------------- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
tip64-sig Linux 2.6.27- 3788 0.17 0.27 1.67 2.65 3.20 0.32 2.97 180. 524. 1806
tip64-sig Linux 2.6.27- 3788 0.17 0.27 1.68 2.65 3.20 0.32 2.95 180. 520. 1796
tip64-sig Linux 2.6.27- 3788 0.17 0.27 1.68 2.72 3.21 0.32 2.96 177. 528. 1812
tip64 Linux 2.6.27- 3788 0.17 0.27 1.68 2.74 3.22 0.32 3.01 174. 523. 1853
tip64 Linux 2.6.27- 3788 0.17 0.27 1.68 2.73 3.22 0.32 3.01 175. 523. 1806
tip64 Linux 2.6.27- 3788 0.17 0.27 1.68 2.74 3.20 0.32 3.01 181. 523. 1791
This patch series also reduces stack usages and code size.
$ size signal_*
text data bss dec hex filename
4507 0 0 4507 119b signal_32.o.new
5031 0 0 5031 13a7 signal_32.o.old
3827 0 0 3827 ef3 signal_64.o.new
4652 0 0 4652 122c signal_64.o.old
Comments are welcome.
I'll handle this patch series if it's good.
thanks,
Hiroshi Shimamoto
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