From mboxrd@z Thu Jan 1 00:00:00 1970 From: Klaas Zweck Subject: Re: About IO-APIC - General question Date: Tue, 16 Apr 2002 13:47:09 +0200 Sender: linux-smp-owner@vger.kernel.org Message-ID: <3CBC0F3D.3010806@tzi.org> References: <3CBBC3D6.1947D011@phys.uni-paderborn.de> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: List-Id: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: "Peter H. Koenig" Cc: linux-smp hi peter, i made some test on a linux-smp machine(kernel 2.4.9). i had one process just doing some calculation on prim numbers. i locked this to cpu 1 and disabled all interrupts on cpu 1. ( in fact i routed all to cpu 0 ) then i started a make -j4 bzImage job in a remote shell to produce file i/o and network interrupts. i restricted all processes except the one doing the calculation from cpu 1 and delivered all interrupts only to cpu 0. i had an total runtime for the calculating process of: (with interrupts routed only to one cpu) voyager:~/# time ./rt_prim_ohne_syscalls real 0m42.111s user 0m41.870s sys 0m0.240s voyager:~/# time ./rt_prim_ohne_syscalls real 0m40.268s user 0m40.190s sys 0m0.080s voyager:~/# time ./rt_prim_ohne_syscalls real 0m40.068s user 0m40.000s sys 0m0.070s average : real: 0m40.815s in the same scenario as above but with irqs routed to all cpus the calculationg process still locked to cpu 1 had a runtime of: voyager:~/# time ./rt_prim_ohne_syscalls -rt real 0m39.712s user 0m39.680s sys 0m0.030s voyager:~/# time ./rt_prim_ohne_syscalls -rt real 0m39.998s user 0m39.720s sys 0m0.270s voyager:~/# time ./rt_prim_ohne_syscalls -rt real 0m39.950s user 0m39.900s sys 0m0.050s average: real 0m39.886s so its a measurable but small performance plus of 2.5 %. but since i worked remote just network and i/o irqs occeured there were no keyboard or mouse irqs in the system. hope it helps a bit, greetings, klaas Peter H. Koenig wrote: >Hello, > >from how I understood APIC it purpose on an SMP machine is to give all >processors the possibility to handle interrupts instead of one processor >responsible for them. So when running two jobs on an SMP machine a >non-working IO-APIC would turn into a performance disadvantage. Do I get >this right ? If yes, does anybody have a clue, how much difference this >could make when running IO-intensive programms ? single or two digit >percentages ? > >Thanks >Pete > > >- >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 >