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option is used (not on by default). - In the case of trying to lock a mutex, if the MTX_CONTESTED flag is set, then we can safely read the thread pointer from the mtx_lock member while holding sched_lock. We then examine the thread to see if it is currently executing on another CPU. If it is, then we keep looping instead of blocking. - In the case of trying to unlock a mutex, it is now possible for a mutex to have MTX_CONTESTED set in mtx_lock but to not have any threads actually blocked on it, so we need to handle that case. In that case, we just release the lock as if MTX_CONTESTED was not set and return. - We do not adaptively spin on Giant as Giant is held for long times and it slows SMP systems down to a crawl (it was taking several minutes, like 5-10 or so for my test alpha and sparc64 SMP boxes to boot up when they adaptively spinned on Giant). - We only compile in the code to do this for SMP kernels, it doesn't make sense for UP kernels. Tested on: i386, alpha, sparc64 |
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| .. | ||
| alpha | ||
| amd64 | ||
| arm | ||
| boot | ||
| cam | ||
| coda | ||
| compat | ||
| conf | ||
| contrib | ||
| crypto | ||
| ddb | ||
| dev | ||
| fs | ||
| geom | ||
| gnu | ||
| i4b | ||
| i386 | ||
| ia64 | ||
| isa | ||
| isofs/cd9660 | ||
| kern | ||
| libkern | ||
| modules | ||
| net | ||
| netatalk | ||
| netatm | ||
| netgraph | ||
| netinet | ||
| netinet6 | ||
| netipx | ||
| netkey | ||
| netnatm | ||
| netncp | ||
| netns | ||
| netsmb | ||
| nfs | ||
| nfsclient | ||
| nfsserver | ||
| pc98 | ||
| pccard | ||
| pci | ||
| posix4 | ||
| powerpc | ||
| rpc | ||
| security/lomac | ||
| sparc64 | ||
| sys | ||
| tools | ||
| ufs | ||
| vm | ||
| Makefile | ||