[uml-devel] [PATCH] commandline switch for sysemu patch

["roland" <for_spam@gmx.de>]

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hi !
I have enhanced laurents sysemu patch a little bit.

the attached patch adds an additional commandline-switch to uml.
if you specify "sysemu" on the commandline, it makes uml use sysemu, if
the host has the sysemu patch,too.
if you don`t specify it, uml doesn`t use sysemu at all.
this makes it easier to compare uml behaviour with and without sysemu (you
don`t need 2 different kernels for that purpose)

Laurent - if you like it, perhaps you could publish that on your website or
include it in your sysemu patch?

regards
roland

ps:
sorry - i have only done it for 2.6.6

pps:
since this is my first patch, maybe this is far from being perfect. feel free
to comment. :)


>Hi,
>
>I put all related information at this URL:
>
>http://perso.wanadoo.fr/laurent.vivier/UML
>
>I have modified the 2.4.24 patches to set PTRACE_SYSEMU to 31 too.
>This modification allows to use 2.4.24 UML on 2.6.6 host, and 2.6.6 UML
>on 2.4.24 host.
>
>Regards,
>Laurent
>
>Le jeu 20/05/2004 à 04:30, roland a écrit :
> Hi Laurent,
> i wondered about:
> "Checking syscall emulation patch for ptrace...missing"
>
> so  - i dig into this:
>
> the uml-patch needs to be adjusted to the fix you gave for the host patch:
> in arch/um/kernel/skas/include/ptrace-skas.h
> i changed :
> #define PTRACE_SYSEMU 25
> to
> #define PTRACE_SYSEMU 31
>
> whoha - now sysemu patch is running with 2.6.6  :)
>
> same positive effect: the getpid loop runs MUCH faster.
> i have tested some other commands and if i run a "vmstat 1" on the HOST,
> i can see the context-swap-rate drop down significantly.
>
> great!
>
> laurent, can you post the sysemu uml and host patch again in ONE mail,
> containing the corrected defines?
> others will probably have it easier this way!
> (maybe some notes about how it works and what it does would be helpful, too)
>
> thanks a lot!
>
> now we need some real-world performance tests/comparisons :)
> regards
> roland
>
> ps:
> i will do some more tests. maybe blaisorblade already wants to mention that
> patch in his 2.6 documentation at: http://www.user-mode-linux.org/~blaisorblade/ ?
>
>
>
>
>
>
> >in include/linux/ptrace.h ,
> >change
> >#define PTRACE_SCEMU            25
> >by
> >#define PTRACE_SCEMU            31
>
>
>
>
>
> ----- Original Message ----- 
> From: "Laurent Vivier" <LaurentVivier@wanadoo.fr>
> To: "roland" <for_spam@gmx.de>
> Cc: <user-mode-linux-devel@lists.sourceforge.net>
> Sent: Wednesday, May 19, 2004 9:49 PM
> Subject: Re: [uml-devel] [PATCH] host context switch reduction
>



[-- Attachment #2: sysemu_cmdline.patch --]
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--- linux-2.6.6/arch/um/kernel/process.c	2004-07-07 06:21:19.144801856 +0200
+++ linux-2.6.6/arch/um/kernel/process.c.sysemu	2004-07-07 06:21:09.136323376 +0200
@@ -41,6 +41,8 @@
 #include "skas_ptrace.h"
 #endif
 
+int sysemu_active=0;
+
 void init_new_thread_stack(void *sig_stack, void (*usr1_handler)(int))
 {
 	int flags = 0, pages;
@@ -230,12 +232,12 @@
 	printk("OK\n");
 
 #ifdef PTRACE_SYSEMU
-	printk("Checking syscall emulation patch for ptrace...");
+       printk("Checking syscall emulation patch for ptrace on HOST...");
 	use_sysemu = 0;
 	pid = start_ptraced_child(&stack);
 	if(ptrace(PTRACE_SYSEMU, pid, 0, 0) >= 0) {
-		struct user_regs_struct regs;
-
+  	 	struct user_regs_struct regs;
+ 
 		if (waitpid(pid, &status, WUNTRACED) < 0)
 			panic("check_ptrace : wait failed, errno = %d", errno);
 		if(!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGTRAP))
@@ -252,18 +254,44 @@
 
 		stop_ptraced_child(pid, stack, 0);
 
-		printk("OK\n");
-		use_sysemu = 1;
-	}
-	else
-	{
-		printk("missing\n");
+		printk("Found!\n");
+                printk("Syscall emulation is...");
+                if(sysemu_active) {
+         	 use_sysemu = 1;
+                 printk("On!\n"); 
+                }           
+                else {
+                 use_sysemu = 0;
+                 printk("Off!\n");  
+                }          
+     
+	 }
+	 else
+	 {
+	 	printk("Missing!\n");
+                if(sysemu_active) {
+                 printk("Notice: You cannot use syscall emulation on this host!\n");
+                }
 		stop_ptraced_child(pid, stack, 1);
-	}
-
+	 }
+        
+        
 # endif /* PTRACE_SYSEMU */
 }
 
+
+static void sysemufnc(char *str)
+{
+ sysemu_active=1;
+}
+
+__uml_setup("sysemu",sysemufnc,
+"sysemu\n    Turn syscall emulation patch for ptrace (SYSEMU) on.\n"
+"    SYSEMU is a performance-patch introduced by Laurent Vivier. It changes\n"
+"    behaviour of ptrace() and helps reducing host context switch rate.\n"
+"    To make it working, you need a kernel patch for your host, too.\n"
+"    See http://perso.wanadoo.fr/laurent.vivier/UML/ for further information.\n\n");
+
 int run_kernel_thread(int (*fn)(void *), void *arg, void **jmp_ptr)
 {
 	jmp_buf buf;