Xorg vs gettimeofday() and clock_gettime()

[Xin LI]

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Coleman Kane wrote:
> Xin LI wrote:
>> John E Hein wrote:
>>> Peter Jeremy wrote at 21:07 +1100 on Feb 26, 2008:
>>>  > My guess is pointer acceleration and/or 3-button emulation.  Out of
>>>  > interest, I just ktrace'd my X server for 5 seconds (doing nothing in
>>>  > particular) and got 318 syscalls, including 106 gettimeofday() calls.
>>>  > By waving the mouse around inside a window, I get 4015 syscalls,
>>>  > including 844 gettimeofday() and 1136 sigprocmask() calls in 5
>>>  > secinds.  In some cases, there are consecutive gettimeofday() calls
>>>  > with no other syscalls intervening.  These numbers do seem somewhat
>>>  > excessive.
>>> Interesting.  
>>> I tried a ktrace session for about 10 seconds _without_ moving the
>>> mouse and got 71332 gettimeofday calls out of 142707 total calls and
>>> signals (all SIGALRM - 2051).
>>> After about 7 minutes with mouse movement (and typing this message), I
>>> saw 193356 gettimeofdays vs 502875 total.
>>> I (obviously) haven't looked at the code.  But perhaps this is an area
>>> that could possibly be improved by more judicious use of select or
>>> kqueue and more independence of interval timing.
>> I think it was some delay call, gettimeofday()s is mostly happen when
>> there is some animations, in the single Xorg process.
>>
>> I will try to make a patch this weekend.  Last weekend I tried to modify
>> only xproto and rebuild dbus and xorg-server, but it seems that it does
>> not like it - with mixed gettimeofday() and clock_gettime(), the display
>> will blank from time to time.
>>
>> Cheers,
> You'll want to remember that clock_gettime returns timspec.tv_nsec
> (nanoseconds), while gettimeofday returns timeval.tv_usec
> (microseconds). In order to perform the conversion, you'll want to make
> sure you convert nanoseconds to microseconds (*1000).

Yes, you're absolutely right, we need to do the conversation, otherwise
the precision of the time would be truncated to second as observed by
the application, which is not good.

Cheers,
- --
Xin LI <delphij at delphij.net>	http://www.delphij.net/
FreeBSD - The Power to Serve!
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