linux-kernel - Re: scheduling anomaly on uml (was: -rt doesn't compile for UML)

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] [day] [month] [year] [list]

Date:	Fri, 30 Nov 2007 20:44:32 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	jdike@...toit.com
CC:	mingo@...e.hu, user-mode-linux-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: scheduling anomaly on uml (was: -rt doesn't compile for UML)

Found some interesting things, the delays are caused by

 1) throttle_vm_writeout()

     I removed it, Andrew worries about that, but hopefully there's a
     better solution to his worries

 2) atime updates

     my uml image did not have them turned off

 3) UML timer tick does not seem very reliable, here's what the below
    patch outputs during writing.  It shows the delay between ticks in
    milliseconds:

[42949415.110000] zzz - 267
[42949415.120000] zzz - 862
[42949415.130000] zzz - 71
[42949415.140000] zzz - 599
[42949415.170000] zzz - 3746
[42949415.190000] zzz - 2961
[42949415.200000] zzz - 3272
[42949415.210000] zzz - 253
[42949415.220000] zzz - 1692
[42949415.230000] zzz - 823
[42949415.280000] zzz - 344
[42949415.310000] zzz - 224

I guess, the ubd interrupts confuse the timekeeping somehow, but the
details are unclear.

Miklos


Index: linux/arch/um/kernel/time.c
===================================================================
--- linux.orig/arch/um/kernel/time.c	2007-11-30 20:19:17.000000000 +0100
+++ linux/arch/um/kernel/time.c	2007-11-30 20:21:24.000000000 +0100
@@ -23,6 +23,12 @@ unsigned long long sched_clock(void)
 void timer_handler(int sig, struct uml_pt_regs *regs)
 {
 	unsigned long flags;
+	static long long last;
+	long long now = os_nsecs() / 1000000;
+
+	if (now - last > 50)
+		printk("zzz - %lli\n", now-last);
+	last = now;
 
 	local_irq_save(flags);
 	do_IRQ(TIMER_IRQ, regs);
-
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/