On 12.06.20 14:29, Julien Grall wrote:
Hi Juergen,
On 12/06/2020 05:57, Jürgen Groß wrote:
On 12.06.20 02:22, Volodymyr Babchuk wrote:
As scheduler code now collects time spent in IRQ handlers and in
do_softirq(), we can present those values to userspace tools like
xentop, so system administrator can see how system behaves.
We are updating counters only in sched_get_time_correction() function
to minimize number of taken spinlocks. As atomic_t is 32 bit wide, it
is not enough to store time with nanosecond precision. So we need to
use 64 bit variables and protect them with spinlock.
Signed-off-by: Volodymyr Babchuk <volodymyr_babc...@epam.com>
---
xen/common/sched/core.c | 17 +++++++++++++++++
xen/common/sysctl.c | 1 +
xen/include/public/sysctl.h | 4 +++-
xen/include/xen/sched.h | 2 ++
4 files changed, 23 insertions(+), 1 deletion(-)
diff --git a/xen/common/sched/core.c b/xen/common/sched/core.c
index a7294ff5c3..ee6b1d9161 100644
--- a/xen/common/sched/core.c
+++ b/xen/common/sched/core.c
@@ -95,6 +95,10 @@ static struct scheduler __read_mostly ops;
static bool scheduler_active;
+static DEFINE_SPINLOCK(sched_stat_lock);
+s_time_t sched_stat_irq_time;
+s_time_t sched_stat_hyp_time;
+
static void sched_set_affinity(
struct sched_unit *unit, const cpumask_t *hard, const cpumask_t
*soft);
@@ -994,9 +998,22 @@ s_time_t sched_get_time_correction(struct
sched_unit *u)
break;
}
+ spin_lock_irqsave(&sched_stat_lock, flags);
+ sched_stat_irq_time += irq;
+ sched_stat_hyp_time += hyp;
+ spin_unlock_irqrestore(&sched_stat_lock, flags);
Please don't use a lock. Just use add_sized() instead which will add
atomically.
add_sized() is definitely not atomic. It will only prevent the compiler
to read/write multiple time the variable.
Oh, my bad, I let myself fool by it being defined in atomic.h.
If we expect sched_get_time_correction to be called concurrently then we
would need to introduce atomic64_t or a spin lock.
Or we could use percpu variables and add the cpu values up when
fetching the values.
Juergen
