tile: nohz: warn if nohz_full uses hypervisor shared cores

The "hypervisor shared" cores are ones that the Tilera hypervisor uses to receive interrupts to manage hypervisor-owned devices. It's a bad idea to try to use those cores with nohz_full, since they will get interrupted unpredictably -- and invisibly to Linux tracing tools, since the interrupts are delivered at a higher privilege level to the Tilera hypervisor. Generate a clear warning at boot up that this doesn't end well for the nohz_full cores in question. Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com>

tile: nohz: warn if nohz_full uses hypervisor shared cores
The "hypervisor shared" cores are ones that the Tilera hypervisor uses to receive interrupts to manage hypervisor-owned devices. It's a bad idea to try to use those cores with nohz_full, since they will get interrupted unpredictably -- and invisibly to Linux tracing tools, since the interrupts are delivered at a higher privilege level to the Tilera hypervisor. Generate a clear warning at boot up that this doesn't end well for the nohz_full cores in question. Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com>
Chris Metcalf
1 parent 437d3e124d
Showing 2 changed files with 28 additions and 1 deletions Side-by-side Diff
arch/tile/include/hv/hypervisor.h
arch/tile/kernel/setup.c
@@ -961,7 +961,11 @@
   HV_INQ_TILES_HFH_CACHE       = 2,
  
   /** The set of tiles that can be legally used as a LOTAR for a PTE. */
-  HV_INQ_TILES_LOTAR           = 3
+  HV_INQ_TILES_LOTAR           = 3,
+
+  /** The set of "shared" driver tiles that the hypervisor may
+   *  periodically interrupt. */
+  HV_INQ_TILES_SHARED          = 4
 } HV_InqTileSet;
  
 /** Returns specific information about various sets of tiles within the
@@ -32,6 +32,7 @@
 #include <linux/hugetlb.h>
 #include <linux/start_kernel.h>
 #include <linux/screen_info.h>
+#include <linux/tick.h>
 #include <asm/setup.h>
 #include <asm/sections.h>
 #include <asm/cacheflush.h>
@@ -1389,6 +1390,28 @@
 }
  
 early_param("dataplane", dataplane);
+
+#ifdef CONFIG_NO_HZ_FULL
+/* Warn if hypervisor shared cpus are marked as nohz_full. */
+static int __init check_nohz_full_cpus(void)
+{
+	struct cpumask shared;
+	int cpu;
+
+	if (hv_inquire_tiles(HV_INQ_TILES_SHARED,
+			     (HV_VirtAddr) shared.bits, sizeof(shared)) < 0) {
+		pr_warn("WARNING: No support for inquiring hv shared tiles\n");
+		return 0;
+	}
+	for_each_cpu(cpu, &shared) {
+		if (tick_nohz_full_cpu(cpu))
+			pr_warn("WARNING: nohz_full cpu %d receives hypervisor interrupts!\n",
+			       cpu);
+	}
+	return 0;
+}
+arch_initcall(check_nohz_full_cpus);
+#endif
  
 #ifdef CONFIG_CMDLINE_BOOL
 static char __initdata builtin_cmdline[COMMAND_LINE_SIZE] = CONFIG_CMDLINE;
...	...	@@ -961,7 +961,11 @@
961	961	HV_INQ_TILES_HFH_CACHE = 2,
962	962
963	963	/** The set of tiles that can be legally used as a LOTAR for a PTE. */
964		- HV_INQ_TILES_LOTAR = 3
	964	+ HV_INQ_TILES_LOTAR = 3,
	965	+
	966	+ /** The set of "shared" driver tiles that the hypervisor may
	967	+ * periodically interrupt. */
	968	+ HV_INQ_TILES_SHARED = 4
965	969	} HV_InqTileSet;
966	970
967	971	/** Returns specific information about various sets of tiles within the
...	...	@@ -32,6 +32,7 @@
32	32	#include <linux/hugetlb.h>
33	33	#include <linux/start_kernel.h>
34	34	#include <linux/screen_info.h>
	35	+#include <linux/tick.h>
35	36	#include <asm/setup.h>
36	37	#include <asm/sections.h>
37	38	#include <asm/cacheflush.h>
...	...	@@ -1389,6 +1390,28 @@
1389	1390	}
1390	1391
1391	1392	early_param("dataplane", dataplane);
	1393	+
	1394	+#ifdef CONFIG_NO_HZ_FULL
	1395	+/* Warn if hypervisor shared cpus are marked as nohz_full. */
	1396	+static int __init check_nohz_full_cpus(void)
	1397	+{
	1398	+ struct cpumask shared;
	1399	+ int cpu;
	1400	+
	1401	+ if (hv_inquire_tiles(HV_INQ_TILES_SHARED,
	1402	+ (HV_VirtAddr) shared.bits, sizeof(shared)) < 0) {
	1403	+ pr_warn("WARNING: No support for inquiring hv shared tiles\n");
	1404	+ return 0;
	1405	+ }
	1406	+ for_each_cpu(cpu, &shared) {
	1407	+ if (tick_nohz_full_cpu(cpu))
	1408	+ pr_warn("WARNING: nohz_full cpu %d receives hypervisor interrupts!\n",
	1409	+ cpu);
	1410	+ }
	1411	+ return 0;
	1412	+}
	1413	+arch_initcall(check_nohz_full_cpus);
	1414	+#endif
1392	1415
1393	1416	#ifdef CONFIG_CMDLINE_BOOL
1394	1417	static char __initdata builtin_cmdline[COMMAND_LINE_SIZE] = CONFIG_CMDLINE;