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This thread is locked; no one can reply to it.
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| a5: problems with timing on eeepc |
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Seppl
Member #4,656
May 2004
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Hi, I just noticed that I'm not using an up-to-date version of a5. But there didn't changed so much concerning timers. Nevertheless I will change to 4.9.12 as soon as I'm home again. Thx __________________________________ |
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Peter Wang
Member #23
April 2000
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The implementation is in src/win/wtime.c (low_res_current_time, high_res_current_time). I would check how the underlying functions perform outside of Allegro. The code hasn't changed for ages so updating Allegro won't make a difference.
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Trent Gamblin
Member #261
April 2000
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The inaccuracy of the timer has been pointed out before. I wonder if it is something wrong with the implementation. It has been noted to be wrong on all platforms.
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X-G
Member #856
December 2000
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I suspect again that this is an issue related to assuming that ticks/seconds remains constant throughout a program's execution, and grows monotonically. This is not the case for multicore systems or system that automatically downstep processor frequency (like the eee). -- |
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Peter Wang
Member #23
April 2000
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Hmm, but which processor doesn't do that any more? Still, you might be right. Can whoever suffers from this problem try to disable the "high_res" timer in wtime.c? It does look a bit dodgy. It's just a small edit to the _al_win_init_time() function.
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Trent Gamblin
Member #261
April 2000
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I tried searching the forums for that sub-bitmap vs. regular bitmap thread but I couldn't find it. The code in that thread didn't work right for me IIRC.
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Peter Wang
Member #23
April 2000
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Presumably that was in response to something else..
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Arthur Kalliokoski
Second in Command
February 2005
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X-G said: This is not the case for multicore systems or system that automatically downstep processor frequency (like the eee) There are at least two timer chips in a PC that have nothing to do with CPU frequency. The frequencies of these are far in excess of what a game demands... They all watch too much MSNBC... they get ideas. |
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Ron Novy
Member #6,982
March 2006
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If possible update the BIOS for your eee pc... Quote from http://download.intel.com/design/processor/specupdt/320047.pdf Quote:
AAG25 Split Locked Stores or Locked Stores Through Certain Segments May not Trigger the Monitoring Hardware Problem: Logical processors normally resume program execution following the MWAIT, when another logical processor performs a write access to a WB cacheable address within the address range used to perform the MONITOR operation. Due to this erratum, a logical processor may not resume execution until the next targeted interrupt event or O/S timer tick following a locked store within the monitored address range that either spans across cache lines or uses a segment register whose segment base is noncacheline aligned. Implication: The logical processor that executed the MWAIT instruction may not resume execution until the next targeted interrupt event or O/S timer tick in the case where the monitored address is written by a locked store which is either split across cache lines or through a segment whose segment base bits 5 to 0 are non-zero. Workaround: Avoid accessing the monitored address range using either locked stores that split cache lines or locked stores that use a segment with a non-cacheline aligned segment base. It is possible for the BIOS to contain a workaround for this erratum Status: For the steppings affected, see the Summary Tables of Changes.
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X-G
Member #856
December 2000
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Arthur Kalliokoski said: There are at least two timer chips in a PC that have nothing to do with CPU frequency. Sure. The problem is that certain methods of measuring time, such as RDTSC and, more oddly, QueryPerformanceCounter (which is odd because QPC is explicitly intended NOT to be subject to the RDTSC issue -- this is mainly a problem, I think, because MSDN's documentation outright lies to you on one critical point), still suffer from the problem and are very commonly used. Not knowing what A5 uses for its high-performance timing, I can't say which one it is; but for timing purposes, anything that relies on CPU clock frequency is no longer an accurate way to do it. -- |
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