Re: [reSIProcate] Timers: why system time?
I think I was to blame for the buggy code and it just had some inline
assembly to use RDTSC instruction.
On May 19, 2009, at 9:00 AM, Justin Matthews wrote:
Do you remember if the buggy code was using RDTSC or
::QueryPerformanceCounter? I believe those have potential issues,
including
changes in CPU frequency. From what I've read I haven't found any
docs
stating that GetTickCount has any of these issues and have not found
any
discussion of related issues. From my own experience
GetTickCount() is not
affected by CPU frequency changes and is always increasing (it's
actually
referenced by Microsoft as a way to keep QPC in-check
(http://support.microsoft.com/default.aspx?scid=KB;EN-US;Q274323).
GetTickCount also works on multiple threads and processors/cores.
Thanks for bringing attention to this. If users are still weary of
it, then
they can continue using the system clock. Another build option may be
useful.
-justin
-----Original Message-----
From: Cullen Jennings [mailto:fluffy@xxxxxxxxx]
Sent: Tuesday, May 19, 2009 10:07 AM
To: Justin Matthews
Cc: 'Scott Godin'; 'Alexander Altshuler'; 'resiprocate-devel'
Subject: Re: [reSIProcate] Timers: why system time?
At one point in time, we had a bug where on machines such a notebook
where the system might step the CPU frequency up or down for power /
performance reasons, we had an issue where the timers got messed up
because they were using clock counts but the the assumption about CPU
frequency was wrong to the time of the timers in seconds was getting
messed up. Whatever you do, make sure you don't reintroduce that bug.
Cullen
On May 19, 2009, at 6:46 AM, Justin Matthews wrote:
Hi,
Attached is a proposed mod to enable monotonic Timer's on Windows
and *unix.
Windows
=========
* _RESIP_WINDOWS_MONOTONIC_CLOCK enables/disables the monotonic
timer. If
disabled, the current ::GetSystemTime is used.
* The default on Windows Vista and beyond is to
use ::GetTickCount64(). No
special handling is required when using this function.
* The default on Windows versions < Vista is
GTCLockDuringRange::GTC64().
This implementation is the one given by Alexander, based on his final
comments below.
* An alternate implementation GTCInterlocked is given and is
intended to
decrease the frequency that the timer must be called and avoid
locking on a
mutex.
* A third alternative is to simply lock each time the timer is called
(GTCLock)
* When not running on Vista or higher, GTCLockDuringRange is the
default
because the GTCInterlocked requires the CMPXCHG8B instruction, which
was
introduced in the intel pentium and AMD K5 and is only supported,
without
assembly, using an intrinsic visual c++ function that is only
available in
visual studio 2005 or higher.
Non-Windows
=========
* _RESIP_POSIX_MONOTONIC_CLOCK enables the __NR_clock_gettime call.
Note
that on some systems even if _POSIX_MONOTONIC_CLOCK is defined
__NR_clock_gettime may not be, or may require another library
(librt?).
Some improvement in enabling this could probably be done in the build
scripts.
=========
Comments?
Thanks,
-justin
-----Original Message-----
From: slgodin@xxxxxxxxx [mailto:slgodin@xxxxxxxxx] On Behalf Of
Scott Godin
Sent: Wednesday, November 05, 2008 2:40 PM
To: Alexander Altshuler
Cc: Justin Matthews; Byron Campen; Adam Roach; resiprocate-devel
Subject: Re: [reSIProcate] Timers: why system time?
I think a solution that does not depend on how often getTimeMs is
called is preferred, given that it doesn't have a huge hit on
performance. This makes the Timer class more usable as a general
utiltiy fn, if used outside of the stack.
Scott
On Wed, Nov 5, 2008 at 2:26 PM, Alexander Altshuler <alt@xxxxxxxxx>
wrote:
Hi All
The requirements for offered Win32 timer wrap around problem:
Timer::getTimeMs() must be reasonable often called.
The solution:
- redefine SipStack::getTimeTillNextProcessMS() that it will return
0xfff maximum for example.
PS: Timer::msTillNextWrapAroundTimer() stuff I posted today will be
unnecessary.
Regards
Alexander Altshuler
http://xeepe.com
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