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Commit 128f3cb9 authored by Chris Metcalf's avatar Chris Metcalf
Browse files

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: default avatarChris Metcalf <cmetcalf@ezchip.com>
parent 437d3e12

arch/tile/include/hv/hypervisor.h

+5 −1
Original line number Diff line number Diff line
@@ -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

arch/tile/kernel/setup.c

+23 −0
Original line number Diff line number Diff line
@@ -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