2c86963b09
Back in January 2008 Nick Piggin implemented "ticket" spinlocks
for X86 (See commit 314cdbefd1).
IA64 implementation has a couple of differences because of the
available atomic operations ... e.g. we have no fetchadd2 instruction
that operates on a 16-bit quantity so we make ticket locks use
a 32-bit word for each of the current ticket and now-serving values.
Performance on uncontended locks is about 8% worse than the previous
implementation, but this seems a good trade for determinism in the
contended case. Performance impact on macro-level benchmarks is in
the noise.
Signed-off-by: Tony Luck <tony.luck@intel.com>
132 lines
3.8 KiB
C
132 lines
3.8 KiB
C
/**
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* @file backtrace.c
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*
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* @remark Copyright 2004 Silicon Graphics Inc. All Rights Reserved.
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* @remark Read the file COPYING
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*
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* @author Greg Banks <gnb@melbourne.sgi.com>
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* @author Keith Owens <kaos@melbourne.sgi.com>
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* Based on work done for the ia64 port of the SGI kernprof patch, which is
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* Copyright (c) 2003-2004 Silicon Graphics Inc. All Rights Reserved.
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*/
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#include <linux/oprofile.h>
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#include <linux/sched.h>
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#include <linux/mm.h>
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#include <asm/ptrace.h>
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#include <asm/system.h>
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/*
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* For IA64 we need to perform a complex little dance to get both
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* the struct pt_regs and a synthetic struct switch_stack in place
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* to allow the unwind code to work. This dance requires our unwind
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* using code to be called from a function called from unw_init_running().
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* There we only get a single void* data pointer, so use this struct
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* to hold all the data we need during the unwind.
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*/
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typedef struct
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{
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unsigned int depth;
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struct pt_regs *regs;
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struct unw_frame_info frame;
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u64 *prev_pfs_loc; /* state for WAR for old spinlock ool code */
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} ia64_backtrace_t;
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/* Returns non-zero if the PC is in the Interrupt Vector Table */
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static __inline__ int in_ivt_code(unsigned long pc)
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{
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extern char ia64_ivt[];
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return (pc >= (u_long)ia64_ivt && pc < (u_long)ia64_ivt+32768);
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}
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/*
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* Unwind to next stack frame.
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*/
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static __inline__ int next_frame(ia64_backtrace_t *bt)
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{
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/*
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* Avoid unsightly console message from unw_unwind() when attempting
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* to unwind through the Interrupt Vector Table which has no unwind
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* information.
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*/
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if (in_ivt_code(bt->frame.ip))
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return 0;
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/*
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* WAR for spinlock contention from leaf functions. ia64_spinlock_contention_pre3_4
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* has ar.pfs == r0. Leaf functions do not modify ar.pfs so ar.pfs remains
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* as 0, stopping the backtrace. Record the previous ar.pfs when the current
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* IP is in ia64_spinlock_contention_pre3_4 then unwind, if pfs_loc has not changed
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* after unwind then use pt_regs.ar_pfs which is where the real ar.pfs is for
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* leaf functions.
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*/
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if (bt->prev_pfs_loc && bt->regs && bt->frame.pfs_loc == bt->prev_pfs_loc)
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bt->frame.pfs_loc = &bt->regs->ar_pfs;
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bt->prev_pfs_loc = NULL;
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return unw_unwind(&bt->frame) == 0;
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}
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static void do_ia64_backtrace(struct unw_frame_info *info, void *vdata)
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{
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ia64_backtrace_t *bt = vdata;
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struct switch_stack *sw;
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int count = 0;
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u_long pc, sp;
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sw = (struct switch_stack *)(info+1);
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/* padding from unw_init_running */
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sw = (struct switch_stack *)(((unsigned long)sw + 15) & ~15);
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unw_init_frame_info(&bt->frame, current, sw);
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/* skip over interrupt frame and oprofile calls */
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do {
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unw_get_sp(&bt->frame, &sp);
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if (sp >= (u_long)bt->regs)
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break;
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if (!next_frame(bt))
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return;
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} while (count++ < 200);
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/* finally, grab the actual sample */
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while (bt->depth-- && next_frame(bt)) {
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unw_get_ip(&bt->frame, &pc);
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oprofile_add_trace(pc);
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if (unw_is_intr_frame(&bt->frame)) {
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/*
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* Interrupt received on kernel stack; this can
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* happen when timer interrupt fires while processing
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* a softirq from the tail end of a hardware interrupt
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* which interrupted a system call. Don't laugh, it
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* happens! Splice the backtrace into two parts to
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* avoid spurious cycles in the gprof output.
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*/
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/* TODO: split rather than drop the 2nd half */
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break;
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}
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}
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}
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void
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ia64_backtrace(struct pt_regs * const regs, unsigned int depth)
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{
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ia64_backtrace_t bt;
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unsigned long flags;
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/*
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* On IA64 there is little hope of getting backtraces from
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* user space programs -- the problems of getting the unwind
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* information from arbitrary user programs are extreme.
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*/
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if (user_mode(regs))
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return;
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bt.depth = depth;
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bt.regs = regs;
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bt.prev_pfs_loc = NULL;
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local_irq_save(flags);
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unw_init_running(do_ia64_backtrace, &bt);
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local_irq_restore(flags);
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}
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