From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Earle R. Nietzel" Subject: Re: SMP questions Date: 19 Jun 2003 23:09:28 +0200 Sender: linux-smp-owner@vger.kernel.org Message-ID: <1056056968.4757.7.camel@home> References: Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Id: Content-Type: text/plain; charset="us-ascii" To: Shreyas Kejariwal Cc: linux-smp On Thu, 2003-06-19 at 18:55, Shreyas Kejariwal wrote: > Thanks Robert. > > Getting back to Q3, as you mentioned, it uses shared bus. So that makes it > hardware specific. However, I read that Posix threads can achieve the same > w/o sharing the bus. Is that correct? > > Can anyone point which dual/SMP processors share memory bus ? > There are some systems that have TLC that are shared between a group fo processors. This how the Unisys ES7000 system works. It has a 32MB TLC shared between each group of 4 processors. This allows SMP to scale better. Unisys has it where you can assign a group (4 processors) to a particular process which will make sure that a hit occurs in the TLC and improves performance for that particular process. Another tweak they allow is to assign I/O devices to a group so that I/O's are occuring in the same processor group as well. > > Shreyas > > > > -- > > ----------------------------------------------- > Shreyas Kejariwal > Perigee LLC > Tel: 315-453 7842 x 42 > > > > "Robert M. Hyatt" wrote in message > news:Pine.LNX.4.44.0306191057030.5678-100000@crafty.cis.uab.edu... > > On Wed, 18 Jun 2003, Shreyas Kejariwal wrote: > > > > > Hi everyone, > > > > > > I am new to this arena and I have few questions so please help me answer > > > them. > > > > > > 1. Looks like most of the new systems employ SMPs. But do we still have > > > ASMPs systems ? > > > > > > If you mean "asymmetric multiprocessing" the answer is generally "no". > > That has pretty much disappeared. If you mean something like clusters > > and so forth, then they are going strong but require different > > programming approaches. > > > > > > > > > > 2. How can we control the tasks, threads to run on a particular > processor ? > > > > Why would you want to? This is something the operating system should > > handle correctly. > > > > > > > Is there a way we can specify ? Take the scenario where there are two > > > multi-threaded applications. I want all the threads of the App1 to run > on > > > Processor, P1 and the threads of the App2 on Processor, P2. Not like > some > > > threads of App1 would run on P2 depending on the scheduler. > > > > > > > > > Most systems support some sort of "processor affinity" stuff, but it is > > a bad idea in general. Leave the O/S stuff to the O/S. It _really_ > > does know better... > > > > > > > > > 3. How can processors access each other's memory / addr space? > > > > > > > Both processors are connected to the memory sub-system with a common > > bus. > > > > > > > > > 4. Digging into the scheduler code, I found that we can either set > scheduler > > > policy to be either Round Robin or FIFO. Are there other schedulers > > > available which use different policy. > > > > > > > What scheduler are you looking at? > > > > > > > > > 5. I read about Shared and Non-shared Cache. How does L2 gets shared. > Its on > > > the die. So does that mean that you have to buy a shared cache board ? > > > > > > > L2 isn't shared on Intel platforms. Each processor has its own L2 cache > > on chip. Otherwise, it is shared just like memory is shared, with a > > common bus connecting it to more than one processor. > > > > > > > > > > > I apologize if some of the questions are stupid and outside the scope of > > > this forum. > > > > > > Moreover, pointers to web-resources would be helpful. > > > > > > Thanks, > > > Shreyas > > > > > > > > > > > > > > > > > > - > > > To unsubscribe from this list: send the line "unsubscribe linux-smp" in > > > the body of a message to majordomo@vger.kernel.org > > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > > > > > -- > > Robert Hyatt Computer and Information Sciences > > hyatt@cis.uab.edu University of Alabama at Birmingham > > (205) 934-2213 115A Campbell Hall, UAB Station > > (205) 934-5473 FAX Birmingham, AL 35294-1170 > > > > - > > To unsubscribe from this list: send the line "unsubscribe linux-smp" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > > > > - > To unsubscribe from this list: send the line "unsubscribe linux-smp" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Earle R. Nietzel