linux-kernel - [PATCH] init: skip calibration delay if previously done

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: Windows password security audit tool. GUI, reports in PDF.

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

Date:	Tue, 24 May 2011 16:19:06 -0700
From:	Sameer Nanda <snanda@...omium.org>
To:	akpm@...ux-foundation.org, ext-phil.2.carmody@...ia.com,
	Tim.Deegan@...rix.com, jbeulich@...ell.com, snanda@...gle.com
Cc:	linux-kernel@...r.kernel.org, Sameer Nanda <snanda@...omium.org>
Subject: [PATCH] init: skip calibration delay if previously done

For each CPU, do the calibration delay only once. For subsequent calls,
use the cached per-CPU value of loops_per_jiffy.

This saves about 200ms of resume time on dual core Intel Atom N5xx based
systems. This helps bring down the kernel resume time on such systems from
about 500ms to about 300ms.

Signed-off-by: Sameer Nanda <snanda@...omium.org>
---
 init/calibrate.c |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/init/calibrate.c b/init/calibrate.c
index 76ac919..47d3408 100644
--- a/init/calibrate.c
+++ b/init/calibrate.c
@@ -183,11 +183,18 @@ recalibrate:
 	return lpj;
 }
 
+DEFINE_PER_CPU(unsigned long, cpu_loops_per_jiffy) = { 0 };
+
 void __cpuinit calibrate_delay(void)
 {
 	static bool printed;
+	int this_cpu = smp_processor_id();
 
-	if (preset_lpj) {
+	if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
+		loops_per_jiffy = per_cpu(cpu_loops_per_jiffy, this_cpu);
+		pr_info("Calibrating delay loop (skipped) "
+				"already calibrated this CPU previously.. ");
+	} else if (preset_lpj) {
 		loops_per_jiffy = preset_lpj;
 		if (!printed)
 			pr_info("Calibrating delay loop (skipped) "
@@ -205,6 +212,7 @@ void __cpuinit calibrate_delay(void)
 			pr_info("Calibrating delay loop... ");
 		loops_per_jiffy = calibrate_delay_converge();
 	}
+	per_cpu(cpu_loops_per_jiffy, this_cpu) = loops_per_jiffy;
 	if (!printed)
 		pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
 			loops_per_jiffy/(500000/HZ),
-- 
1.7.3.1

--
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/