From 383f2835eb9afb723af71850037b2f074ac9db60 Mon Sep 17 00:00:00 2001 From: "Chen, Kenneth W" Date: Fri, 9 Sep 2005 13:02:02 -0700 Subject: [PATCH] [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: Ken Chen Cc: Ingo Molnar Cc: "Luck, Tony" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/ia64/kernel/entry.S | 23 +++++++++++++++++++++++ include/asm-ia64/system.h | 1 + include/linux/sched.h | 5 +++++ kernel/sched.c | 1 + 4 files changed, 30 insertions(+) diff --git a/arch/ia64/kernel/entry.S b/arch/ia64/kernel/entry.S index 3c88210245..915e127918 100644 --- a/arch/ia64/kernel/entry.S +++ b/arch/ia64/kernel/entry.S @@ -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 diff --git a/include/asm-ia64/system.h b/include/asm-ia64/system.h index 33256db4a7..635235fa1e 100644 --- a/include/asm-ia64/system.h +++ b/include/asm-ia64/system.h @@ -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); diff --git a/include/linux/sched.h b/include/linux/sched.h index ea1b5f32ec..c551e6a144 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -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; diff --git a/kernel/sched.c b/kernel/sched.c index 18b95520a2..2632b812cf 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -2888,6 +2888,7 @@ switch_tasks: 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)); -- 2.39.5