gettimeofday order of magnitude slower with pmtimer, which is default

From: bert hubert
Date: Mon Mar 20 2006 - 07:22:09 EST

Hi everybody,

For my open source nameserver ( 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 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

This problem has been discussed before

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?


-- Open source, database driven DNS Software Open and Closed source services
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