Date: Thu, 8 Jan 2009 16:08:08 +0100 From: Ulf Lilleengen <ulf.lilleengen@gmail.com> To: Mehmet Ali Aksoy =?iso-8859-1?B?VNxZU9xa?= <aksoy.for.research@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: Threads and SMP kernel scheduling Message-ID: <20090108150807.GA1264@carrot.pvv.ntnu.no> In-Reply-To: <14ded62c0901080123u7268055epb3e17d84aa757051@mail.gmail.com> References: <14ded62c0901080123u7268055epb3e17d84aa757051@mail.gmail.com>
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On Thu, Jan 08, 2009 at 04:23:08AM -0500, Mehmet Ali Aksoy TÜYSÜZ wrote: > Hi all, > > After I had a bit googling I got confused. > > My questions are simple and they are as follows : > > 1-) "Are pthreads (or threads in general) of one process scheduled to > different cores on multi-core systems running Linux or BSD?" > The standard threading library in FreeBSD will use a 1:1 mapping between userland threads(pthreads) and kernel threads. This means that each thread may run on a different core than other threads. > 2-) What if there are multiple processes which have multiple threads? Does > it change the answer of (1)? No, the same mapping applies. Although threads of one process may preferably run on the same core, each thread of a process may run on any of the cores available. > > I found some answers but they are not sharp. Somebody says "can be > scheduled" but "can be" is not a precise answer (in my opinion.) Well, it means that there are more factors deciding where a thread is put. If you look at a factor such as affinity, one thread may preferable be scheduled to the same core since the cache may contain data relevant to the thread. > > Thanks everybody in advance. > Hope everything is at least a bit clearer. -- Ulf Lilleengen
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