From: Chris Metcalf <cmetc...@ezchip.com>
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 <cmetc...@ezchip.com>
---
arch/tile/include/hv/hypervisor.h | 6 +++++-
arch/tile/kernel/setup.c | 23 +++++++++++++++++++++++
2 files changed, 28 insertions(+), 1 deletion(-)
diff --git a/arch/tile/include/hv/hypervisor.h
b/arch/tile/include/hv/hypervisor.h
index dfcdeb61ba34..e0e6af4e783b 100644
--- a/arch/tile/include/hv/hypervisor.h
+++ b/arch/tile/include/hv/hypervisor.h
@@ -961,7 +961,11 @@ typedef enum {
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
diff --git a/arch/tile/kernel/setup.c b/arch/tile/kernel/setup.c
index f1f579914952..7833b2ccdfbc 100644
--- a/arch/tile/kernel/setup.c
+++ b/arch/tile/kernel/setup.c
@@ -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>
@@ -1390,6 +1391,28 @@ static int __init dataplane(char *str)
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;
#endif
--
2.1.2
--
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