linux-kernel - [PATCH 2/7] cputime: Remove extra cost in task

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1447948054-28668-3-git-send-email-fweisbec@gmail.com>
Date:	Thu, 19 Nov 2015 16:47:29 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Chris Metcalf <cmetcalf@...hip.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Luiz Capitulino <lcapitulino@...hat.com>,
	Christoph Lameter <cl@...ux.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>, stable@...r.kernel.org,
	Rik van Riel <riel@...hat.com>
Subject: [PATCH 2/7] cputime: Remove extra cost in task_cputime

From: Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>

There is an extra cost in task_cputime() and task_cputime_scaled() when
nohz_full is not activated. When vtime accounting is not enabled, we
don't need to get deltas of utime and stime under vtime seqlock.

This patch removes that cost with adding a shortcut route if vtime
accounting is not enabled.

Use context_tracking_is_enabled() to check if vtime is accounting on
some cpu, in which case only we need to check the tickless cputime delta.

Signed-off-by: Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
Cc: stable@...r.kernel.org
Cc: Christoph Lameter <cl@...ux.com>
Cc: Chris Metcalf <cmetcalf@...hip.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Luiz Capitulino <lcapitulino@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rik van Riel <riel@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
---
 kernel/sched/cputime.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 05de80b..1128d4b 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -853,6 +853,14 @@ void task_cputime(struct task_struct *t, cputime_t *utime, cputime_t *stime)
 {
 	cputime_t udelta, sdelta;
 
+	if (!context_tracking_is_enabled()) {
+		if (utime)
+			*utime = t->utime;
+		if (stime)
+			*stime = t->stime;
+		return;
+	}
+
 	fetch_task_cputime(t, utime, stime, &t->utime,
 			   &t->stime, &udelta, &sdelta);
 	if (utime)
@@ -866,6 +874,14 @@ void task_cputime_scaled(struct task_struct *t,
 {
 	cputime_t udelta, sdelta;
 
+	if (!context_tracking_is_enabled()) {
+		if (utimescaled)
+			*utimescaled = t->utimescaled;
+		if (stimescaled)
+			*stimescaled = t->stimescaled;
+		return;
+	}
+
 	fetch_task_cputime(t, utimescaled, stimescaled,
 			   &t->utimescaled, &t->stimescaled, &udelta, &sdelta);
 	if (utimescaled)
-- 
2.5.3

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/