linux-kernel - [PATCH][resubmit] x86: enable preemption in delay

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

Date:	Sun, 1 Jun 2008 19:01:23 +0300
From:	Marin Mitov <mitov@...p.bas.bg>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-rt-users <linux-rt-users@...r.kernel.org>, akpm@...l.org,
	Ingo Molnar <mingo@...e.hu>,
	Clark Williams <clark.williams@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	Gregory Haskins <ghaskins@...ell.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi-suse@...stfloor.org>
Subject: [PATCH][resubmit] x86: enable preemption in delay

Hi all,

This is a resubmit of the patch proposed by Ingo and me
few month ago:

http://lkml.org/lkml/2007/11/20/343

It was in -mm for a while and then removed due to a move into
the mainline, but it never appeared in it.

As recently a new discussion started on the subject I decided
to resubmit it again.

Now it is against 2.6.25.4, but as far as there are no changes 
in the modified files it should apply to 2.6.26-rc4 too.

Comments/critics are wellcome.

Marin Mitov


Signed-off-by: Marin Mitov <mitov@...p.bas.bg>
Signed-off-by: Ingo Molnar <mingo@...e.hu>

=========================================
--- a/arch/x86/lib/delay_32.c	2007-11-18 08:14:05.000000000 +0200
+++ b/arch/x86/lib/delay_32.c	2007-11-20 19:03:52.000000000 +0200
@@ -40,18 +40,42 @@
 		:"0" (loops));
 }
 
-/* TSC based delay: */
+/* TSC based delay:
+ *
+ * We are careful about preemption as TSC's are per-CPU.
+ */
 static void delay_tsc(unsigned long loops)
 {
-	unsigned long bclock, now;
+	unsigned prev, prev_1, now;
+	unsigned left = loops;
+	unsigned prev_cpu, cpu;
+
+	preempt_disable();
+	rdtscl(prev);
+	prev_cpu = smp_processor_id();
+	preempt_enable();
+	now = prev;
 
-	preempt_disable();		/* TSC's are per-cpu */
-	rdtscl(bclock);
 	do {
 		rep_nop();
+
+		left -= now - prev;
+		prev = now;
+
+		preempt_disable();
+		rdtscl(prev_1);
+		cpu = smp_processor_id();
 		rdtscl(now);
-	} while ((now-bclock) < loops);
-	preempt_enable();
+		preempt_enable();
+
+		if (prev_cpu != cpu) {
+			/*
+			 * We have migrated, forget prev_cpu's tsc reading
+			 */
+			prev = prev_1;
+			prev_cpu = cpu;
+		}
+	} while ((now-prev) < left);
 }
 
 /*
--- a/arch/x86/lib/delay_64.c	2007-11-18 08:14:40.000000000 +0200
+++ b/arch/x86/lib/delay_64.c	2007-11-20 19:47:29.000000000 +0200
@@ -28,18 +28,42 @@
 	return 0;
 }
 
+/* TSC based delay:
+ *
+ * We are careful about preemption as TSC's are per-CPU.
+ */
 void __delay(unsigned long loops)
 {
-	unsigned bclock, now;
+	unsigned prev, prev_1, now;
+	unsigned left = loops;
+	unsigned prev_cpu, cpu;
+
+	preempt_disable();
+	rdtscl(prev);
+	prev_cpu = smp_processor_id();
+	preempt_enable();
+	now = prev;
 
-	preempt_disable();		/* TSC's are pre-cpu */
-	rdtscl(bclock);
 	do {
-		rep_nop(); 
+		rep_nop();
+
+		left -= now - prev;
+		prev = now;
+
+		preempt_disable();
+		rdtscl(prev_1);
+		cpu = smp_processor_id();
 		rdtscl(now);
-	}
-	while ((now-bclock) < loops);
-	preempt_enable();
+		preempt_enable();
+
+		if (prev_cpu != cpu) {
+			/*
+			 * We have migrated, forget prev_cpu's tsc reading
+			 */
+			 prev = prev_1;
+			 prev_cpu = cpu;
+		}
+	} while ((now-prev) < left);
 }
 EXPORT_SYMBOL(__delay);
 
-



--
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/