Date: Fri, 06 Nov 1998 12:06:35 -0800 From: Mike Smith <mike@smith.net.au> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: David Greenman <dg@root.com>, cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG Subject: Re: sendfile.2 (was Re: cvs commit: ...) Message-ID: <199811062006.MAA00469@dingo.cdrom.com> In-Reply-To: Your message of "Fri, 06 Nov 1998 10:05:10 PST." <199811061805.KAA00657@apollo.backplane.com>
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> > The interesting thing about this is that the number of context switches > does not seem to be the deciding factor... otherwise I would have expected > the blocking write() case to have a more significant spread. Instead, > it appears to be the actual switch to and from user mode that is causing > the greatest overhead. The block-write() case does not return to usermode > while the non-blocking sendfile() case does. Either that, or select()ing > on a single descriptor is more expensive then I thought it was. That's about consistent with expectations; context switch from one process context to another is about as fast as it can be. Crossing the user:kernel protection boundary is not so easy - one of the major shortcomings of the i386 architecture it seems. -- \\ Sometimes you're ahead, \\ Mike Smith \\ sometimes you're behind. \\ mike@smith.net.au \\ The race is long, and in the \\ msmith@freebsd.org \\ end it's only with yourself. \\ msmith@cdrom.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message
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