Date: Sat, 8 Jul 2000 18:13:38 -0700 (PDT) From: hsu@FreeBSD.ORG (Jeffrey Hsu) To: jdp@FreeBSD.ORG Cc: freebsd-arch@FreeBSD.ORG Subject: yield(2) (was Re: cvs commit: src/libexec/rtld-elf rtld.c rtld.h lockdflt.c) Message-ID: <20000709011338.880E337BA97@hub.freebsd.org>
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Spinlocks are the only kinds of locks that work with all thread packages. But on uniprocessor systems they can be inefficient, because while a contender for the lock is spinning the holder of the lock cannot make any progress toward releasing it. To alleviate this disadvantage I have borrowed a trick from Sleepycat's Berkeley DB implementation. When spinning for a lock, the requester does a nanosleep() call for 1 usec. each time around the loop. This will generally yield the CPU to other threads, allowing the lock holder to finish its business and release the lock. What do you think of adding a real yield(2) system call? I do the nanosleep too in some locking code I use for a pre-forked server (like Apache), but I am unhappy with that. I chosed 100ms as the sleep time because that's one scheduler quantum (or used to be). It wasn't clear to me that a nanosleep of anything less than a quantum would guarantee a yield. Jeffrey To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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