提交 383f2835 编写于 作者: C Chen, Kenneth W 提交者: Linus Torvalds

[PATCH] Prefetch kernel stacks to speed up context switch

For architecture like ia64, the switch stack structure is fairly large
(currently 528 bytes).  For context switch intensive application, we found
that significant amount of cache misses occurs in switch_to() function.
The following patch adds a hook in the schedule() function to prefetch
switch stack structure as soon as 'next' task is determined.  This allows
maximum overlap in prefetch cache lines for that structure.
Signed-off-by: NKen Chen <kenneth.w.chen@intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: "Luck, Tony" <tony.luck@intel.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
上级 b0d62e6d
......@@ -470,6 +470,29 @@ ENTRY(load_switch_stack)
br.cond.sptk.many b7
END(load_switch_stack)
GLOBAL_ENTRY(prefetch_stack)
add r14 = -IA64_SWITCH_STACK_SIZE, sp
add r15 = IA64_TASK_THREAD_KSP_OFFSET, in0
;;
ld8 r16 = [r15] // load next's stack pointer
lfetch.fault.excl [r14], 128
;;
lfetch.fault.excl [r14], 128
lfetch.fault [r16], 128
;;
lfetch.fault.excl [r14], 128
lfetch.fault [r16], 128
;;
lfetch.fault.excl [r14], 128
lfetch.fault [r16], 128
;;
lfetch.fault.excl [r14], 128
lfetch.fault [r16], 128
;;
lfetch.fault [r16], 128
br.ret.sptk.many rp
END(prefetch_switch_stack)
GLOBAL_ENTRY(execve)
mov r15=__NR_execve // put syscall number in place
break __BREAK_SYSCALL
......
......@@ -275,6 +275,7 @@ extern void ia64_load_extra (struct task_struct *task);
*/
#define __ARCH_WANT_UNLOCKED_CTXSW
#define ARCH_HAS_PREFETCH_SWITCH_STACK
#define ia64_platform_is(x) (strcmp(x, platform_name) == 0)
void cpu_idle_wait(void);
......
......@@ -604,6 +604,11 @@ extern int groups_search(struct group_info *group_info, gid_t grp);
#define GROUP_AT(gi, i) \
((gi)->blocks[(i)/NGROUPS_PER_BLOCK][(i)%NGROUPS_PER_BLOCK])
#ifdef ARCH_HAS_PREFETCH_SWITCH_STACK
extern void prefetch_stack(struct task_struct*);
#else
static inline void prefetch_stack(struct task_struct *t) { }
#endif
struct audit_context; /* See audit.c */
struct mempolicy;
......
......@@ -2888,6 +2888,7 @@ asmlinkage void __sched schedule(void)
if (next == rq->idle)
schedstat_inc(rq, sched_goidle);
prefetch(next);
prefetch_stack(next);
clear_tsk_need_resched(prev);
rcu_qsctr_inc(task_cpu(prev));
......
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