Full quote for Debian Bug Tracking System bugnumber 504495 ( http://bugs.debian.org/504495 )
Op 20090503 om 00:58 schreef Peter Iannucci: > H. Peter Anvin wrote: >> Peter Iannucci wrote: >> >>> Hello hpa, >>> >>> We are developing a Xen-based virtualization service, and we are trying >>> to reduce excessive CPU utilization at isolinux boot prompts. When >>> users boot up a virtual machine on an isolinux boot CD, the CPU starts >>> spinning at 100%. These machines frequently get left in this state for >>> days or weeks, degrading the service for everyone else. >>> >>> You replied to the work-around discussed in the earlier thread at >>> >>> http://syslinux.zytor.com/archives/2005-June/005291.html >>> >>> >>>> Breaks serial console. >>>> -hpa >>>> >>> In our case, the serial console is not an issue. We would like to >>> submit a patch to isolinux which HLTs on getchar if isolinux is not >>> running with the serial console option. Do you think this is the right >>> solution to this problem? Can we work with you to resolve this? >>> >>> >> >> It would *probably* be okay to do when serial console is not enabled, >> but it seems a bit crude... and also it's somewhat confusing that one >> should enable serial console and get drastically different behavior. >> >> What is much more confusing to me is why do you have VMs left like this >> for "days or weeks"? It is about wasted resources. That used to be a non-issue, but now on virtualisation we have to pay ... >> -hpa >> > One improvement might be enabling interrupts for the serial port. On > line 1277 of 2.6.29/drivers/serial/8250.c, this is accomplished with > > serial_outp(up, UART_IER, 0x0f); > > where the UART Interrupt Enable Register is defined on line 23 of > include/linux/serial_reg.h, and serial_outp is responsible for > special-casing unusual devices. The protocol for enabling interrupts > via this register is common to all standard PC serial ports (and can > easily be scraped from 8250.c for exceptions as desired). > > On scanning through syslinux/core/parseconfig.inc, it looks like the > infrastructure for enabling serial IRQ's is already present, but is not > being used. Once these interrupts are enabled, the HLT should take care > of both cases fine. Proposal: Introduce a configuration keyword named like 'halt_on_idle'. 'halt_on_idle' is optional and when set is HLT used in the "idle loop" that waits for a key stroke. > By way of explanation, when our users boot a VM with a live CD and > reboot from within the guest, the domain still has the CD still > attached. This leaves the machine spinning at the boot prompt. Users > forget and leave their machines in this state frequently enough that it > has become a problem. Similarly, users occasionally create a new VM and > specify a first-time boot CD, but never log in to complete the install. > It only takes a few VMs using 100% of a CPU to degrade the performance > of a host. Probably should 'halt_on_idle' be default and is a 'no_halt_on_idle' or a 'active_poll' needed. 'active_poll' has to be mentioned in de section 'serial port' of the docs. > -Peter Iannucci Cheers Geert Stappers -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
