Author: Matt Taylor
Date: 11:56:01 02/20/03
Go up one level in this thread
On February 20, 2003 at 11:31:04, Robert Hyatt wrote: >On February 20, 2003 at 02:49:04, Matt Taylor wrote: > >>On February 19, 2003 at 20:05:30, Robert Hyatt wrote: >> >>>On February 19, 2003 at 18:28:12, Charles Worthington wrote: >>> >>>>Bob I am not a programmer. Can you direct me to a source that will enable me to >>>>make the tweaks on the Fritz Spinlocks and Spinwaits myself? Getting chessbase >>>>to do anything would be near impossible. >>> >>> >>>No. It is a source code modification, which is the problem. You _might_ be >>>able to use a debugger and find the spinlocks, but inserting a pause instruction >>>might not be possible as it will mean "stretching" the code which would break >>>things without some cute tricks, such as a jump out to the lock and a jump >>>back... >>> >>>I wouldn't want to think about it not having any idea where the locks really >>>are. :) >> >>It wouldn't be too difficult with a good knowledge of assembly and some good >>tools. Profile for highly localized hotspots (there are your spinlocks) and then >>use code stretching to insert code. I wrote a tool at work that does this for >>Windows programs, but it requires PDB information. I know of no tool on the >>market that is capable of code stretching without such information. >> >>Realistically he might as well ask nicely. :-) >> >>-Matt > > >That might work. However, the spinlocks (in crafty) don't get burned a lot, due >to the way >it is designed in attempting to minimize locking. It might well be possible to >miss a few that >don't get beat on in the particular run. I guess I shouldn't have called them hotspots. I was thinking of any short loop. Most do some sort of computation, so most wouldn't be seen as spinlocks. Alternatively you could search for pause (if it uses it) or the lock prefix. Perhaps look for the bts/btr or xchg instructions inside the loop. You -might- incur false positives, but I doubt there would be many. >As I said, it is doable. I used to have to patch operating systems like that >all the time, where >you need to insert code, which means you replace a good instruction with a jump >to a patch >area, stick the replaced instruction plus the ones you need to add there, >followed by a jump >back to where you came from. > >But it is not for the non-ASM person, obviously. Yes, you can do it like that. I was talking about recompilation, which is a much slicker trick. You have to move code around to insert your own, and that's what makes it a pain to do. My own tool still breaks in some cases because it can't guarantee that it will find all function pointers. If you miss a function pointer, the code obviously is going to break. Your method is definitely easier without nice tools. In performance-optimized applications, functions are going to be 16-byte aligned, too. That will leave a fair amount of CCh (int3) or 90h (nop) space to use. If you can find small functions in a relatively small area, you can use the 2-byte jump form, too. -Matt
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