[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, 10 insertions, 20 deletions

diff --git a/arch/um/os-Linux/process.c b/arch/um/os-Linux/process.c
index 39815c6b5e45..7f5e2dac2a35 100644
--- a/arch/um/os-Linux/process.c
+++ b/arch/um/os-Linux/process.c
@@ -18,6 +18,7 @@
 #include "process.h"
 #include "irq_user.h"
 #include "kern_util.h"
+#include "longjmp.h"
 
 #define ARBITRARY_ADDR -1
 #define FAILURE_PID    -1
@@ -205,24 +206,13 @@ void init_new_thread_signals(int altstack)
 
 int run_kernel_thread(int (*fn)(void *), void *arg, void **jmp_ptr)
 {
-       sigjmp_buf buf;
-       int n;
-
-       *jmp_ptr = &buf;
-       n = sigsetjmp(buf, 1);
-       if(n != 0)
-               return(n);
-       (*fn)(arg);
-       return(0);
+        sigjmp_buf buf;
+        int n, enable;
+
+        *jmp_ptr = &buf;
+        n = UML_SIGSETJMP(&buf, enable);
+        if(n != 0)
+                return(n);
+        (*fn)(arg);
+        return(0);
 }
-
-/*
- * Overrides for Emacs so that we follow Linus's tabbing style.
- * Emacs will notice this stuff at the end of the file and automatically
- * adjust the settings for this buffer only.  This must remain at the end
- * of the file.
- * ---------------------------------------------------------------------------
- * Local variables:
- * c-file-style: "linux"
- * End:
- */