[RFC PATCH v2 5/7] Documentation: Add three sysctls for smart idle poll

Yang Zhang
2017-08-29T11:48:21Z

To reduce the cost of poll, we introduce three sysctl to control the
poll time.

Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com>
Signed-off-by: Quan Xu <quan.xu0@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Alok Kataria <akataria@vmware.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: "Luis R. Rodriguez" <mcgrof@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jessica Yu <jeyu@redhat.com>
Cc: Larry Finger <Larry.Finger@lwfinger.net>
Cc: zijun_hu <zijun_hu@htc.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Johannes Berg <johannes.berg@intel.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: virtualization@lists.linux-foundation.org
Cc: linux-fsdevel@vger.kernel.org
---
Documentation/sysctl/kernel.txt | 25 +++++++++++++++++++++++++
arch/x86/kernel/paravirt.c | 4 ++++
include/linux/kernel.h | 6 ++++++
kernel/sysctl.c | 23 +++++++++++++++++++++++
4 files changed, 58 insertions(+)

diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index bac23c1..67447b8 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -63,6 +63,9 @@ show up in /proc/sys/kernel:
- perf_event_max_stack
- perf_event_max_contexts_per_stack
- pid_max
+- poll_grow [ X86 only ]
+- poll_shrink [ X86 only ]
+- poll_threshold_ns [ X86 only ]
- powersave-nap [ PPC only ]
- printk
- printk_delay
@@ -702,6 +705,28 @@ kernel tries to allocate a number starting from this one.

==============================================================

+poll_grow: (X86 only)
+
+This parameter is multiplied in the grow_poll_ns() to increase the poll time.
+By default, the values is 2.
+
+==============================================================
+poll_shrink: (X86 only)
+
+This parameter is divided in the shrink_poll_ns() to reduce the poll time.
+By default, the values is 2.
+
+==============================================================
+poll_threshold_ns: (X86 only)
+
+This parameter controls the max poll time before entering real idle path.
+This parameter is expected to take effect only when running inside a VM.
+It would make no sense to turn on it in bare mental.
+By default, the values is 0 means don't poll. It is recommended to change
+the value to non-zero if running latency-bound workloads inside VM.
+
+==============================================================
+
powersave-nap: (PPC only)

If set, Linux-PPC will use the 'nap' mode of powersaving,
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index a11b2c2..0b92f8f 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -318,6 +318,10 @@ struct pv_idle_ops pv_idle_ops = {
.update = paravirt_nop,
};

+unsigned long poll_threshold_ns;
+unsigned int poll_shrink = 2;
+unsigned int poll_grow = 2;
+
__visible struct pv_irq_ops pv_irq_ops = {
.save_fl = __PV_IS_CALLEE_SAVE(native_save_fl),
.restore_fl = __PV_IS_CALLEE_SAVE(native_restore_fl),
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index bd6d96c..6cb2820 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -462,6 +462,12 @@ extern __scanf(2, 0)

extern bool crash_kexec_post_notifiers;

+#ifdef CONFIG_PARAVIRT
+extern unsigned long poll_threshold_ns;
+extern unsigned int poll_shrink;
+extern unsigned int poll_grow;
+#endif
+
/*
* panic_cpu is used for synchronizing panic() and crash_kexec() execution. It
* holds a CPU number which is executing panic() currently. A value of
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 6648fbb..9b86a8f 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1229,6 +1229,29 @@ static int sysrq_sysctl_handler(struct ctl_table *table, int write,
.extra2 = &one,
},
#endif
+#ifdef CONFIG_PARAVIRT
+ {
+ .procname = "halt_poll_threshold",
+ .data = &poll_threshold_ns,
+ .maxlen = sizeof(unsigned long),
+ .mode = 0644,
+ .proc_handler = proc_dointvec,
+ },
+ {
+ .procname = "halt_poll_grow",
+ .data = &poll_grow,
+ .maxlen = sizeof(unsigned int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec,
+ },
+ {
+ .procname = "halt_poll_shrink",
+ .data = &poll_shrink,
+ .maxlen = sizeof(unsigned int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec,
+ },
+#endif
{ }
};

--
1.8.3.1