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[SPARC64]: Make save_stack_trace() more efficient.

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Doing a 'flushw' every stack trace capture creates so much overhead
that it makes lockdep next to unusable.

We only care about the frame pointer chain and the function caller
program counters, so flush those by hand to the stack frame.

This is significantly more efficient than a 'flushw' because:

1) We only save 16 bytes per active register window to the stack.

2) This doesn't push the entire register window context of the current
   call chain out of the cpu, forcing register window fill traps as we
   return back down.

Note that we can't use 'restore' and 'save' instructions to move
around the register windows because that wouldn't work on Niagara
processors.  They optimize 'save' into a new register window by
simply clearing out the registers instead of pulling them in from
the on-chip register window backing store.

Based upon a report by Tom Callaway.

Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David S. Miller 2008-03-24 20:06:24 -07:00
parent 6d00815323
commit 85a7935335
3 changed files with 39 additions and 1 deletions
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30
arch/sparc64/kernel/entry.S
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@ -1705,6 +1705,36 @@ __flushw_user:
2: retl
nop
/* Flush %fp and %i7 to the stack for all register
* windows active inside of the cpu. This allows
* show_stack_trace() to avoid using an expensive
* 'flushw'.
*/
.globl stack_trace_flush
.type stack_trace_flush,#function
stack_trace_flush:
rdpr %pstate, %o0
wrpr %o0, PSTATE_IE, %pstate
rdpr %cwp, %g1
rdpr %canrestore, %g2
sub %g1, 1, %g3
1: brz,pn %g2, 2f
sub %g2, 1, %g2
wrpr %g3, %cwp
stx %fp, [%sp + STACK_BIAS + RW_V9_I6]
stx %i7, [%sp + STACK_BIAS + RW_V9_I7]
ba,pt %xcc, 1b
sub %g3, 1, %g3
2: wrpr %g1, %cwp
wrpr %o0, %pstate
retl
nop
.size stack_trace_flush,.-stack_trace_flush
#ifdef CONFIG_SMP
.globl hard_smp_processor_id
hard_smp_processor_id:

4
arch/sparc64/kernel/stacktrace.c
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@ -2,13 +2,15 @@
#include <linux/stacktrace.h>
#include <linux/thread_info.h>
#include <asm/ptrace.h>
#include <asm/stacktrace.h>
void save_stack_trace(struct stack_trace *trace)
{
unsigned long ksp, fp, thread_base;
struct thread_info *tp = task_thread_info(current);
flushw_all();
stack_trace_flush();
__asm__ __volatile__(
"mov %%fp, %0"
: "=r" (ksp)

6
include/asm-sparc64/stacktrace.h Normal file
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@ -0,0 +1,6 @@
#ifndef _SPARC64_STACKTRACE_H
#define _SPARC64_STACKTRACE_H
extern void stack_trace_flush(void);
#endif /* _SPARC64_STACKTRACE_H */