Messages in this thread |  | | | Date | Mon, 20 Mar 2006 13:24:49 +0100 | | From | bert hubert <> | | Subject | gettimeofday order of magnitude slower with pmtimer, which is default |
| |
Hi everybody,
For my open source nameserver (http://www.powerdns.com) I need to do quite a number of gettimeofday calls. I've pared it down to almost the bare minimum of 1 gettimeofday per packet sent and received. With these calls, I can make stats like http://ds9a.nl/tmp/rrd/ which my users need so they can verify the proper performance of the nameserver.
Yesterday, together with Zwane, I discovered each gettimeofday call costs me 4 usec on some boxes and almost nothing on others. We did a fruitless chase for vsyscall/sysenter happening but the problem turned out to be CONFIG_X86_PM_TIMER.
This problem has been discussed before http://www.ussg.iu.edu/hypermail/linux/kernel/0411.1/2135.html
Not only is the pm timer slow by design, it also needs to be read multiple times to work around a bug in certain hardware.
What is new is that this option is now dependent on CONFIG_EMBEDDED. Unless you select this option, the PM Timer will always be used.
Would a patch removing the link to EMBEDDED and adding a warning that while this timer is of high quality, it is slow, be welcome?
Thanks.
-- http://www.PowerDNS.com Open source, database driven DNS Software http://netherlabs.nl Open and Closed source services - 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/
|  |