Messages in this thread Patch in this message | | | Date | Thu, 19 Jul 2007 17:42:54 +0200 | From | Ingo Molnar <> | Subject | [patch] sched: implement cpu_clock(cpu) high-speed time source |
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* Jeremy Fitzhardinge <jeremy@goop.org> wrote:
> > yeah. But then it should not be using sched_clock() but CFS's new > > rq_clock() method - which does try to construct a globally valid > > timesource out of sched_clock(). [that fix is not backportable > > though] > > Hm, that doesn't look quite right. Doesn't rq_clock measure time > spent running? Unstolen time includes idle time too (it just excludes > time in which a VCPU is runnable but not actually running).
generally rq_clock() also includes idle time, so it should work fine for this purpose. So, what do you think about the patch below - does it suit Xen's purposes?
Ingo
--------------------> Subject: sched: implement cpu_clock(cpu) high-speed time source From: Ingo Molnar <mingo@elte.hu>
Implement the cpu_clock(cpu) interface for kernel-internal use: high-speed (but slightly incorrect) per-cpu clock constructed from sched_clock().
fix up blktrace and softlockup-watchdog to use this new interface.
Signed-off-by: Ingo Molnar <mingo@elte.hu> --- block/blktrace.c | 20 ++++++++++---------- include/linux/sched.h | 7 +++++++ kernel/sched.c | 17 +++++++++++++++++ kernel/softlockup.c | 10 ++++++---- 4 files changed, 40 insertions(+), 14 deletions(-)
Index: linux/block/blktrace.c =================================================================== --- linux.orig/block/blktrace.c +++ linux/block/blktrace.c @@ -41,7 +41,7 @@ static void trace_note(struct blk_trace const int cpu = smp_processor_id(); t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION; - t->time = sched_clock() - per_cpu(blk_trace_cpu_offset, cpu); + t->time = cpu_clock(cpu) - per_cpu(blk_trace_cpu_offset, cpu); t->device = bt->dev; t->action = action; t->pid = pid; @@ -159,7 +159,7 @@ void __blk_add_trace(struct blk_trace *b t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION; t->sequence = ++(*sequence); - t->time = sched_clock() - per_cpu(blk_trace_cpu_offset, cpu); + t->time = cpu_clock(cpu) - per_cpu(blk_trace_cpu_offset, cpu); t->sector = sector; t->bytes = bytes; t->action = what; @@ -488,17 +488,17 @@ void blk_trace_shutdown(request_queue_t } /* - * Average offset over two calls to sched_clock() with a gettimeofday() + * Average offset over two calls to cpu_clock() with a gettimeofday() * in the middle */ -static void blk_check_time(unsigned long long *t) +static void blk_check_time(unsigned long long *t, int this_cpu) { unsigned long long a, b; struct timeval tv; - a = sched_clock(); + a = cpu_clock(this_cpu); do_gettimeofday(&tv); - b = sched_clock(); + b = cpu_clock(this_cpu); *t = tv.tv_sec * 1000000000 + tv.tv_usec * 1000; *t -= (a + b) / 2; @@ -510,16 +510,16 @@ static void blk_check_time(unsigned long static void blk_trace_check_cpu_time(void *data) { unsigned long long *t; - int cpu = get_cpu(); + int this_cpu = get_cpu(); - t = &per_cpu(blk_trace_cpu_offset, cpu); + t = &per_cpu(blk_trace_cpu_offset, this_cpu); /* * Just call it twice, hopefully the second call will be cache hot * and a little more precise */ - blk_check_time(t); - blk_check_time(t); + blk_check_time(t, this_cpu); + blk_check_time(t, this_cpu); put_cpu(); } Index: linux/include/linux/sched.h =================================================================== --- linux.orig/include/linux/sched.h +++ linux/include/linux/sched.h @@ -1327,6 +1327,13 @@ static inline int set_cpus_allowed(struc #endif extern unsigned long long sched_clock(void); + +/* + * For kernel-internal use: high-speed (but slightly incorrect) per-cpu + * clock constructed from sched_clock(): + */ +extern unsigned long long cpu_clock(int cpu); + extern unsigned long long task_sched_runtime(struct task_struct *task); Index: linux/kernel/sched.c =================================================================== --- linux.orig/kernel/sched.c +++ linux/kernel/sched.c @@ -365,6 +365,23 @@ static inline unsigned long long rq_cloc } /* + * For kernel-internal use: high-speed (but slightly incorrect) per-cpu + * clock constructed from sched_clock(): + */ +unsigned long long cpu_clock(int cpu) +{ + struct rq *rq = cpu_rq(cpu); + unsigned long long now; + unsigned long flags; + + spin_lock_irqsave(&rq->lock, flags); + now = rq_clock(rq); + spin_unlock_irqrestore(&rq->lock, flags); + + return now; +} + +/* * The domain tree (rq->sd) is protected by RCU's quiescent state transition. * See detach_destroy_domains: synchronize_sched for details. * Index: linux/kernel/softlockup.c =================================================================== --- linux.orig/kernel/softlockup.c +++ linux/kernel/softlockup.c @@ -41,14 +41,16 @@ static struct notifier_block panic_block * resolution, and we don't need to waste time with a big divide when * 2^30ns == 1.074s. */ -static unsigned long get_timestamp(void) +static unsigned long get_timestamp(int this_cpu) { - return sched_clock() >> 30; /* 2^30 ~= 10^9 */ + return cpu_clock(this_cpu) >> 30; /* 2^30 ~= 10^9 */ } void touch_softlockup_watchdog(void) { - __raw_get_cpu_var(touch_timestamp) = get_timestamp(); + int this_cpu = raw_smp_processor_id(); + + per_cpu(touch_timestamp, this_cpu) = get_timestamp(this_cpu); } EXPORT_SYMBOL(touch_softlockup_watchdog); @@ -94,7 +96,7 @@ void softlockup_tick(void) return; } - now = get_timestamp(); + now = get_timestamp(this_cpu); /* Wake up the high-prio watchdog task every second: */ if (now > (touch_timestamp + 1)) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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