Date: Wed, 26 Mar 2003 09:18:45 +0100 From: Miguel Mendez <flynn@energyhq.homeip.net> To: alex@dynaweb.ru Cc: FreeBSD hackers list <freebsd-hackers@freebsd.org> Subject: Re: Some specific questions about 5.x Message-ID: <20030326091845.36425fad.flynn@energyhq.homeip.net> In-Reply-To: <3E815D53.6010404@dynaweb.ru> References: <3E815D53.6010404@dynaweb.ru>
next in thread | previous in thread | raw e-mail | index | archive | help
--=.N0y:iHrl5Oj6r3 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 26 Mar 2003 10:57:07 +0300 Alex <alex@dynaweb.ru> wrote: Howdy. > 1. Is it true that kernel threads are more "heavy" than userspace > ones (pthread) and hence application with hundreds of threads will > work evidently slower than that using pthreads due to more switching > penalties? AFAIK, not in a hybrid model. Systems that do 1:1 thread mapping (Like Gah! Nu/Linux) will suffer from this kind of situation, also will use more kernel memory. In hybrid implementations based on Scheduler Activations, like FreeBSD's KSE, and NetBSD's SA, there's a balance between the number of kernel virtual processors available and the number of userland threads, it's an N:M model. Nathan Williams' paper on the subject suggests that context switch is not much slower than a pure userland implementation. Also, keep in mind that pure userland has other problems, like when one thread blocks on I/O. In pure userland threading systems this means the whole process is blocked, whereas in KSE and SA only that thread is stopped. > 2. Is it true that even 5.x has no implementation for inter-process > semaphores that are blocking calling thread only not the whole process > as usually in FreeBSD? That I don't know, perhaps the local KSE guru, Julian might have an answer for this. Cheers, -- Miguel Mendez - flynn@energyhq.homeip.net GPG Public Key :: http://energyhq.homeip.net/files/pubkey.txt EnergyHQ :: http://www.energyhq.tk Tired of Spam? -> http://www.trustic.com --=.N0y:iHrl5Oj6r3 Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.1 (NetBSD) iD8DBQE+gWJpnLctrNyFFPERAjBRAJ9XdUgcfg8DMVqRVKq3cposKYuMqQCgrNhC XfQS2H+jgl9hNTe2vtJp1go= =4k59 -----END PGP SIGNATURE----- --=.N0y:iHrl5Oj6r3--
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20030326091845.36425fad.flynn>