Messages in this thread Patch in this message | | | Subject | Re: scheduling anomaly on uml (was: -rt doesn't compile for UML) | From | Miklos Szeredi <> | Date | Fri, 30 Nov 2007 20:44:32 +0100 |
| |
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@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |