Re: [PATCH v7 02/11] task_isolation: add initial support

On 10/01/2015 08:14 AM, Frederic Weisbecker wrote:

On Mon, Sep 28, 2015 at 11:17:17AM -0400, Chris Metcalf wrote:

quoted

diff --git a/include/linux/isolation.h b/include/linux/isolation.h
new file mode 100644
index 000000000000..fd04011b1c1e
--- /dev/null
+++ b/include/linux/isolation.h

@@ -0,0 +1,24 @@
+/*
+ * Task isolation related global functions
+ */
+#ifndef _LINUX_ISOLATION_H
+#define _LINUX_ISOLATION_H
+
+#include <linux/tick.h>
+#include <linux/prctl.h>
+
+#ifdef CONFIG_TASK_ISOLATION
+static inline bool task_isolation_enabled(void)
+{
+	return tick_nohz_full_cpu(smp_processor_id()) &&
+		(current->task_isolation_flags & PR_TASK_ISOLATION_ENABLE);

Ok, I may be a bit burdening with that but, how about using the regular
existing task flags, and if needed later we can still introduce a new field
in struct task_struct?

The problem is still that we have two basic bits ("enabled" and
"strict") plus eight bits of signal number to override SIGKILL.
So we end up with *something* extra in task_struct no matter what.
And, right now it's conveniently the same value as the bits
passed to prctl(), so we don't need to marshall and unmarshall
the prctl() get/set results.

If we could convince ourselves not to do the "settable signal"
stuff I'd agree that use task flags makes sense, but I was
convinced for v2 of the patch series to add a settable signal,
and I suspect it still does make sense.

quoted

+	while (READ_ONCE(dev->next_event.tv64) != KTIME_MAX) {

You should add a function in tick-sched.c to get the next tick. This
is supposed to be a private field.

Yes.  Or probably better, a function that just says whether the
timer is quiesced.  Obviously I'll wait to hear what Thomas says
on this subject first, though.

quoted

+		if (!warned && (jiffies - start) >= (5 * HZ)) {
+			pr_warn("%s/%d: cpu %d: task_isolation task blocked for %ld seconds\n",
+				task->comm, task->pid, smp_processor_id(),
+				(jiffies - start) / HZ);
+			warned = true;
+		}
+		cond_resched();
+		if (test_thread_flag(TIF_SIGPENDING))
+			break;

Why not use signal_pending()?

Makes sense, thanks.

I still think we could try a wait-wake standard scheme. 

I'm curious to hear what you make of my arguments in the
other thread on this subject!

-- 
Chris Metcalf, EZChip Semiconductor
http://www.ezchip.com