[PATCH] uml: implement soft interrupts

This patch implements soft interrupts.  Interrupt enabling and disabling no
longer map to sigprocmask.  Rather, a flag is set indicating whether
interrupts may be handled.  If a signal comes in and interrupts are marked as
OK, then it is handled normally.  If interrupts are marked as off, then the
signal handler simply returns after noting that a signal needs handling.  When
interrupts are enabled later on, this pending signals flag is checked, and the
IRQ handlers are called at that point.

The point of this is to reduce the cost of local_irq_save et al, since they
are very much more common than the signals that they are enabling and
disabling.  Soft interrupts produce a speed-up of ~25% on a kernel build.

Subtleties -

    UML uses sigsetjmp/siglongjmp to switch contexts.  sigsetjmp has been
    wrapped in a save_flags-like macro which remembers the interrupt state at
    setjmp time, and restores it when it is longjmp-ed back to.

    The enable_signals function has to loop because the IRQ handler
    disables interrupts before returning.  enable_signals has to return with
    signals enabled, and signals may come in between the disabling and the
    return to enable_signals.  So, it loops for as long as there are pending
    signals, ensuring that signals are enabled when it finally returns, and
    that there are no pending signals that need to be dealt with.

Signed-off-by: Jeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 17 insertions, 12 deletions

diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
index b959b2618b7f8..120a21c5883f6 100644
--- a/arch/um/os-Linux/skas/process.c
+++ b/arch/um/os-Linux/skas/process.c
@@ -34,6 +34,7 @@
 #include "mem.h"
 #include "uml-config.h"
 #include "process.h"
+#include "longjmp.h"
 
 int is_skas_winch(int pid, int fd, void *data)
 {
@@ -433,6 +434,7 @@ void new_thread(void *stack, void **switch_buf_ptr, void **fork_buf_ptr,
 {
 	unsigned long flags;
 	sigjmp_buf switch_buf, fork_buf;
+	int enable;
 
 	*switch_buf_ptr = &switch_buf;
 	*fork_buf_ptr = &fork_buf;
@@ -447,7 +449,7 @@ void new_thread(void *stack, void **switch_buf_ptr, void **fork_buf_ptr,
 	 */
 	flags = get_signals();
 	block_signals();
-	if(sigsetjmp(fork_buf, 1) == 0)
+	if(UML_SIGSETJMP(&fork_buf, enable) == 0)
 		new_thread_proc(stack, handler);
 
 	remove_sigstack();
@@ -458,20 +460,22 @@ void new_thread(void *stack, void **switch_buf_ptr, void **fork_buf_ptr,
 void thread_wait(void *sw, void *fb)
 {
 	sigjmp_buf buf, **switch_buf = sw, *fork_buf;
+	int enable;
 
 	*switch_buf = &buf;
 	fork_buf = fb;
-	if(sigsetjmp(buf, 1) == 0)
+	if(UML_SIGSETJMP(&buf, enable) == 0)
 		siglongjmp(*fork_buf, INIT_JMP_REMOVE_SIGSTACK);
 }
 
 void switch_threads(void *me, void *next)
 {
 	sigjmp_buf my_buf, **me_ptr = me, *next_buf = next;
+	int enable;
 
 	*me_ptr = &my_buf;
-	if(sigsetjmp(my_buf, 1) == 0)
-		siglongjmp(*next_buf, 1);
+	if(UML_SIGSETJMP(&my_buf, enable) == 0)
+		UML_SIGLONGJMP(next_buf, 1);
 }
 
 static sigjmp_buf initial_jmpbuf;
@@ -484,14 +488,14 @@ static sigjmp_buf *cb_back;
 int start_idle_thread(void *stack, void *switch_buf_ptr, void **fork_buf_ptr)
 {
 	sigjmp_buf **switch_buf = switch_buf_ptr;
-	int n;
+	int n, enable;
 
 	set_handler(SIGWINCH, (__sighandler_t) sig_handler,
 		    SA_ONSTACK | SA_RESTART, SIGUSR1, SIGIO, SIGALRM,
 		    SIGVTALRM, -1);
 
 	*fork_buf_ptr = &initial_jmpbuf;
-	n = sigsetjmp(initial_jmpbuf, 1);
+	n = UML_SIGSETJMP(&initial_jmpbuf, enable);
 	switch(n){
 	case INIT_JMP_NEW_THREAD:
 		new_thread_proc((void *) stack, new_thread_handler);
@@ -501,7 +505,7 @@ int start_idle_thread(void *stack, void *switch_buf_ptr, void **fork_buf_ptr)
 		break;
 	case INIT_JMP_CALLBACK:
 		(*cb_proc)(cb_arg);
-		siglongjmp(*cb_back, 1);
+		UML_SIGLONGJMP(cb_back, 1);
 		break;
 	case INIT_JMP_HALT:
 		kmalloc_ok = 0;
@@ -512,20 +516,21 @@ int start_idle_thread(void *stack, void *switch_buf_ptr, void **fork_buf_ptr)
 	default:
 		panic("Bad sigsetjmp return in start_idle_thread - %d\n", n);
 	}
-	siglongjmp(**switch_buf, 1);
+	UML_SIGLONGJMP(*switch_buf, 1);
 }
 
 void initial_thread_cb_skas(void (*proc)(void *), void *arg)
 {
 	sigjmp_buf here;
+	int enable;
 
 	cb_proc = proc;
 	cb_arg = arg;
 	cb_back = &here;
 
 	block_signals();
-	if(sigsetjmp(here, 1) == 0)
-		siglongjmp(initial_jmpbuf, INIT_JMP_CALLBACK);
+	if(UML_SIGSETJMP(&here, enable) == 0)
+		UML_SIGLONGJMP(&initial_jmpbuf, INIT_JMP_CALLBACK);
 	unblock_signals();
 
 	cb_proc = NULL;
@@ -536,13 +541,13 @@ void initial_thread_cb_skas(void (*proc)(void *), void *arg)
 void halt_skas(void)
 {
 	block_signals();
-	siglongjmp(initial_jmpbuf, INIT_JMP_HALT);
+	UML_SIGLONGJMP(&initial_jmpbuf, INIT_JMP_HALT);
 }
 
 void reboot_skas(void)
 {
 	block_signals();
-	siglongjmp(initial_jmpbuf, INIT_JMP_REBOOT);
+	UML_SIGLONGJMP(&initial_jmpbuf, INIT_JMP_REBOOT);
 }
 
 void switch_mm_skas(struct mm_id *mm_idp)