Date: Thu, 20 Dec 2001 15:12:01 -0800 (PST) From: John Baldwin <jhb@FreeBSD.org> To: Anthony Atkielski <anthony@freebie.atkielski.com> Cc: Jeremiah Gowdy <jeremiah@sherline.com>, advocacy@FreeBSD.org, Gilbert Gong <ggong@cal.alumni.berkeley.edu> Subject: Re: Microsoft Advocacy? Message-ID: <XFMail.011220151201.jhb@FreeBSD.org> In-Reply-To: <02b601c189aa$632a5990$0a00000a@atkielski.com>
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On 20-Dec-01 Anthony Atkielski wrote: > John writes: > >> Atomic operations are _quite_ expensive. On >> x86, they lock the bus which means waiting until >> the bus is free. > > How much time do you gain, percentage-wise, in the routines in which locks > have been eliminated? On x86, atomic operations can take 100's of clock cycles in comparison with zero when you dont' have to do the move at all. Not that lack of load/modify/store is always faster than doing the operation. :) Also, note that it is on if you have any sort of lock debugging turned on. >> If you really care, first go look at some >> actual code to see where these things are >> used and how ... > > Any suggestions on modules to examine? Any of the scheduler code in current. sys/kern/kern_synch.c (as well as sys/kern/kern_intr.c:ithread_schedule() to see what we do for a hardware interrupt). To see how mutexes are implemented, sys/sys/mutex.h, and sys/kern/kern_mutex.c. The atomic manpage (man 9 atomic) on current will also be helpful in grokking this stuff. Also, for a good reference about how locking works in Unix, you can read the books 'Unix for Modern Architectures: Symmetric Multiprocessing and Caching for Kernel Programmers' by Curt Schemmel (I may have botched the name) or 'Unix Internals: The New Frontiers' by Uresh Vahalia. For a brief overview of the types of locks used in -current, you can also read my paper about the subject in the BSDCon proceedings. -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-advocacy" in the body of the message
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